Author Topic: Plastic color, discoloration & restoration: Chemical treatment vs Layer Removal  (Read 780 times)

Offline TelePlay

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Found this moss green WE 500 in a box that was packed up and set aside many years ago. Probably bought it because it was cheap and had an open center finger wheel implying it was possibly soft plastic. Inspection of the phone showed it to be a mixed date ABS phone that was dirty, inside and out, and someone had painted the housing with a cheap spray paint.

The phone was tested and found to be fully functional out of the box. At that point, the decision was simply what to do with the phone. Being a working phone with paint that could be easily removed, it was decided to restore the phone.

While the paint was soft and easily removed using any of a few means, the plastic under the paint was a discolored dark green. ABS when exposed to UV light changes color and the physical properties of the plastic are also changed. The discolored plastic becomes very hard and impervious to chemical sanding – pure acetone on a cotton cloth would not easily dissolve and remove the age darkened plastic surface.

This hard surface layer has been seen before in other housings but in this case, it was harder and more difficult to remove than any other phone worked on in the past. As such, the only way to remove the discolored plastic would be to sand it off.

Sanding, other than having to navigate all of the inside curves and corners of a 500 housing, is a good way to get rid of the paint, the discolored plastic and any dings and/or scratches on the housing.  Sanding also took off the residual glue left on the housing by fiber reinforced strapping tape seen above the dial bezel.

Sanding resulted in a very nice, unscratched ABS housing in its original color. Getting  from the painted, dirty housing to the final restoration product was an interesting adventure which showed a few things about plastic discoloration. The following points out what was discovered and is followed by information learned about color and plastic discoloration.

You can click on the following images to see the detail.
« Last Edit: January 20, 2020, 11:02:31 PM by TelePlay »

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Re: Practical plastic discoloration analysis
« Reply #1 on: January 13, 2020, 08:24:54 PM »
Chemical treatment vs. surface layer removal

( the following is the edited body of a PM sent to a member discussing chemical treatment using an oxidizer versus physical/chemical sanding for the removal of age related plastic discoloration )

As for using an oxidizer for chemical treatment of discolored plastic, the salon care developer is the right stuff. If has a long shelf light and being a creme mixture, it stays on the plastic rather, does not run off, as a watery mixture would. You only need to use the amount necessary to cover the plastic. Volume developers are not an immersion process. Vol 20 may be a bit weak. You can read the link at the post below for information on creme developers and decide for yourself which you want to use. You can buy it in a smaller quart bottle at your local Sally Beauty Supply store. It's inexpensive, a little goes a long way and it has a long shelf life. I bought Vol 20 and 40 so I could use them as is or mix them together to get 30.

That topic started with "what polish to use" and turned into a chemical treatment topic at this link in the topic. You may want to read the topic from this point on to learn more about chemical treatment of discolored plastic.


Now, as for this type of restoration work, there is a lot of information posted on the forum from 2009 to about 2018. Chemical treatment means the use of a strong oxidizing chemical, bleach or peroxide (salon hair care stuff or the retrobrite formula), to get rid of the discoloration.

Chemical treatment is a process that causes a chemical reaction on the plastic's surface, a reaction is hoped will reverse the chemical reaction that took place over many years due to inherent bonding degradation, atmospheric conditions, light and cleaners/polishes coming into contact with the plastic. UV light discoloration is easy to spot in that one side of the phone, the phone facing the sun light, will have received more UV light over the years and discolored more that other areas on the phone.

Chemical treatment using an oxidizing agent is not an exact science and without getting into the reaction that changes pi-level orbital bonding in this PM, the result from the use of chemicals varies from the chemical used to the plastic it is used on. Every housing came from a different batch of plastic and how that batch was mixed to come up with surface pi-bonding that created a desired reflective color is unknown and different from batch to batch. Over time, the pi-bonds are broken by any or all processes mentioned above and the color changes, the plastic becomes discolored. What color the original plastic changes to, the discoloration, depends on how the pi-bonds are broken and/or re-arranged and the length of the time over which the bonding degradation took place.

From experience reported in forum topics, some colors are improved by using an oxidation reaction using bleaching or peroxide and some are made worse. It seems lighter original colors are better "restored" with chemicals than darker colors which are made worse. Blue, red and green, from what I remember being posted, are not good candidates for chemical treatment. White, ivory, beige and pink can be improved to some extent. Not sure about yellow but probably a good candidate.

I don't want to get into the physical chemistry of reflective color generation in this PM other than to say that discoloration is the original plastic color being changed over time as its surface pi-bonds are changed. Changes to what color and cast is a function of the external agent (including UV light) hitting the surface, the length of time, the strength of the external agent and the plastic mixture originally poured/cast.

Bleach and peroxide are merely external agents of another type that produce a chemical reaction that only affects or changes in some way the very thin layer of the plastic's surface. After the treatment, that thin surface layer becomes free to once again change, to discolor, due to chemical changes in the "restored" plastic by way of inherent bonding degradation (the stability of a color change due to use of an oxidizing agent is suspect), atmospheric agents and conditions, light and cleaners/polishes.

I tried to restore a pink housing (shown below) some time ago using peroxide.

After treatment (left image) it looked good. I put the phone in a box and 6 months later discovered it was back to the salmon color that the peroxide "removed" during chemical treatment. The chemical change in the surface color by treating it with peroxide reverted back to the darker, salmon color in a short period of time, and in a dark box.

Over time, I've seen moss green change to a darker green, pink change to a salmon color, beige and ivory getting darker and blue change to a greenish yellow tint. AE made an orchid colored phone which was notorious for changing to blue over time (discolored image below). It was thought that the dyes and/or pigments themselves used to create the orchid color were unstable an more easily degraded over time. You can see the original orchid color inside the housing and handset in the second image below. This phone would have to be physically sanded to get back to the original color. There is no amount or type of chemical treatment that would improve this phone, make it look like it did right out of its mold.

Below is an example of an orchid AE phone in the process of discoloration. Chemical treatment probably would not work on this housing either in that the purple changing to blue chromophores are uneven in concentration across the surface (discolor variation) and chemical treatment reacts evenly on the entire surface at the same time.

The only real (time consuming and tedious) way to get any phone back to it's original color is to physically remove the discolored surface layer by paper and/or chemical sanding.

As for a step by step procedure for chemical treatment method to remove discoloration, it's nothing more than cleaning the plastic surface to make sure no oils or waxes are present which would keep the bleach/peroxide from getting to all of the plastic evenly. Oils and waxes will prevent the oxidizing agent from reaching the surface. When using the peroxide creme oxidizer, a phone housing will fit into a 2 gallon Ziploc bag (freezer bags are better in that the plastic bag is thicker and less prone to tear).  The salon volume developer is added to the bag, which ever volume is thought to be needed. Volume 30 is a good starting point. Simply close the bag and smoosh the creme all over the outside of the housing. Set the bag in a warm area under either sun light or in a UV light box. Every 10 minutes, re-smoosh the creme on the body to prevent splotches due to an uneven chemical reaction. Peroxide needs warmth and UV radiation in sunlight to activate the chemical reaction (a warm spot is needed along with UV light in sunlight to activate the peroxide molecules that come into contact with the plastic - a foaming may appear which is the breakdown of peroxide into water and oxygen with oxygen being the chemical reaction that affects the discolored plastic. If using sunlight, it is important to turn the housing every 10 minutes (when re-smooshing) to provide even amount of light exposure to the entire housing during the treatment period. It is also important to pay attention to housing areas, such as cradle ears, which always seem to be in the light and as such can be over exposed and lead to over lightening of the ears.

After a period of time, the color change can be seen through the bag and when the desired color is reached, simply take the housing or plastic part out of the bag and rinse it off. Dry the housing and check the color. If not happy with it, put it back into the bag, add more of the creme and repeat the exposure/smooshing cycle. You may have to add or change the peroxide in that it does wear out, it breaks down, and no longer produces oxygen. In a warm area with bright sun light, this process can achieve the desired color change in a few hours or less.

Bleach is similar to peroxide creme in that it also oxidized the plastic surface. Household chlorine bleach also produces oxygen in a similar but different chemical reaction. Bleach water seems to work with or without sunlight. It seems the best environment is warm bleach water and sun light to speed up the reaction between the released oxygen and the plastic's surface.  Bleaching will react in the dark as long as the temperature of the bath is a warm room temperate, say 80 to 90 degrees F. Liquid bleach is diluted with warm water in a tub or pail large enough for a phone housing to be submerged. Since the bleach bath is bleach mixed with water, there is not need to smoosh it around but stirring the bath every 10 minutes is recommended to prevent "hot spots" from appearing on the plastic. If the water mixture (distilled water and bleach) is stirred, the concentration of bleach will always be the same on all parts of the plastic. Distilled water is recommended in that no one knows what is in tap water and what affect it may have on the bleach reaction on plastic. Depending on the plastic itself, the amount of discoloration, the temperature of the bath, the use of UV light and the concentration of bleach in the bath, bleaching could take anywhere from an hour to many hours. The housing should be removed from the bleach bath periodically to check it progress. When satisfied with the color change, remove and rinse with water.

With peroxide or bleach, it's a trial and error process. I suggest searching for and reading the good topics posted on the forum by members who have successfully used chemical processing to adjust discolored plastic and to note those topics reporting that a color was ruined using chemicals. Ruined plastic usually means a splotchy surface or undesired color was created by oxidizing the plastic's surface, and in those cases, all is not lost. One can always sand off the outer "ruined" layer to get back to the original plastic color. Discolored plastic is a very thin surface layer and the original plastic in the original color can be restored by sanding off the outer layer, discolored layer.

It has also been noted that the chemical changes in the the plastic which cause discoloration also changes the physical properties properties of the plastic. I have many times found that the discolored surface layer to be a very hard plastic resistant to both chemical and paper sanding. While the original ABS plastic dissolves quickly in pure acetone, a discolored surface disolves very slowly with pure acetone on a cotton cloth and sanding required a smaller grit to cut through this hardened plastic. As soon as that discolored layer is removed, the underlying original plastic sands well, as expected, with higher grit paper or chemicals (pure acetone on original color ABS is very aggressive and pure acetone on discolored ABS plastic has little affect).

I had a severely damage soft plastic ivory 302 housing (and the physical effect of a handset cup shielding the housing from discoloration can be seen in the red circle in the image below).

The surface on two sides turned a crispy, toasted brown. I broke off a few pieces of that housing and put them in pure acetone. The inside of the chips dissolved away in a few hours leaving the toasted brown surface intact, undissolved. After more than 2 years in that acetone bath, the toasted brown surface has still not dissolved.

That is proof positive that the chemical change that occurs on the surface to produce discoloration also hardens the plastic, makes it something other than ABS. The polymer become glass-like with the increased hardness resistant to solvents, which would normally dissolve the plastic quickly, and sanding.

Plasticizers, their role is plastic hardness

There is another type of chemical, in general called plasticizers, that is added to polymerized plastics to give the plastic certain physical properties. This would include making the plastic softer, more flexible than the pure plastic polymer and increase the flow and thermoplasticity of a polymer by decreasing the plastics viscosity when in melted form (easier to inject into a mold). There are chemical groups of plasticizers and the decision to use which one with some plastic to achieve a certain result is complex.

Plasticizers are usually inert organic materials with high boiling points and low vapor pressures. Esters are commonly used due to their favorable physical interactions with high-molecular-weight polymers. These are the chemicals that interact with the polymer to increase its flexibility. One plastic supplier said "The mechanical properties of plastics differ with plasticizer levels. Lower plasticizer content yields a harder surface, higher heat resistance, greater rigidity, higher tensile strength, and better dimensional stability. Higher plasticizer content increases impact strength." It could be the case that an external agent, such as UV light, which causes discoloration can also degrade the plasticizers and in doing so make the surface plastic harder and less flexible. That may be why the underlying, original plastic beneath the hardened, discolored surface layer not only retains its original color but also retains its original "softness" (lower resistance to solvents) and flexibility, or less brittle and we all know that old plastic becomes more brittle and breaks more easily.

Over time, there are several factors which can lead to migration of plasticizer out of plastics surface such as temperature change, humidity change, mechanical stress,  and weathering. This is seen in old telephone cords becoming stiff and brittle to the point of cracking. Since phone plastic that is not discolored is also not hardened, it seems that something is happening along with discoloration that also breaks down or removes the plasticizers from the surface of the plastic making it harder, or solvent and sanding resistant compared to non-discolored plastic on the same housing (the inside, for example).

A common example of plastic with and with out a plasticizer is rigid and non-rigid PVC. Unplasticized PVC (or rigid PVC) is used in applications such as pipes, siding, and window profiles while plasticized PVC (or flexible PVC) finds applications in automotive interior trim, cables, PVC films, flooring, roofing and wall coverings. It seems that phone plastic in the process of being discolored also suffers a loss of its plasticizers, at the surface, making color restoration (regardless of method) more difficult.

Chemical treatment, as the means to remove discoloration, is a trial and error method when first starting to use either bleach or peroxide (including retro-brite). It is possible to test the bleach or peroxide on the inside of the housing to see what they will do to the color, to the plastic. While the inside will not be discolored, this test can determine if either oxidizing agent will harm the plastic. And even after doing that test, there is no guarantee of what will happen when using that agent on the housing since the exterior plastic will already have been chemically changed (it's been discolored) so using the tested chemical agent on the exterior may not react the same was as it did on an interior spot.

The above is being sent to you in a PM because, while I want to give you what I know, I want your topic to hopefully generate replies from others, not be ended by a long reply from me. I'm not sure how many members are still around that have done restoration of discolored plastics using chemical treatment but most of their pioneering work has been posted on the forum. Getting someone to give you a step by step will be difficult in that each person developed their own procedure, each may be slightly different and many won't take the time to share their work if not already posted.


A few weeks ago, I paper sanded a moss green 500 housing that was painted grey. I used paper because of the paint, the scratches in the housing and the hardened dark green surface plastic that was resistant to acetone.

Below are the before, in process and after images. This image shows the 5 layers of color that were on this housing. In the center image and above the dial hole from left to right, you can see fiber strapping tape residue that looks light green due to is capturing sanding dust. To the right of that is the gray paint. To the right of the gray paint you can see a yellow plastic which is plastic that was color changed, discolored, by the solvents in the paint. Next comes the hardened darker green typical of WE moss green phones and to the right of that, the original ABS moss green plastic (which looks very light with its 320 grit surface texture). The image to the right is the completely sanded housing which was sanded up from 320 grit surface to 2,000 grit and then final polishing with Novus 2. The sanding process removed all discoloration, all scratches,all dings and revealed the original moss green color (chemical treatment does not remove scratches and dings).

The darkened, discolored moss green layer was so hard in some places (due to more exposure to UV sunlight) that I ended up using 80 grit wet sandpaper to cut through it. That took off the paint, the hardened dark green surface and the scratches (180 and then 320 grit paper was used to get the housing ready for 400 grit paper). Once the hardened plastic was removed, sanding the original, softer green ABS plastic up to 2000 took a very short time. The entire housing was sanded up from 320 to 2000 in about 3 hours.

The reason the 320 grit surface looks so light is a function of random light reflection. Once polished smooth, the reflected light is quite ordered, uniform, parallel while shows, to the eye, only the light from each part of the surface, not scattered light from all over the surface due to rough sanding marks which makes it look lighter. All of these images were taken under the same light source with the same camera.

The image below shows a badly discolored blue phone (handset and bezel show green) that I restored by physically sanding off the handset and bezel. That made the original ABS blue plastic, just beneath the discolored surface layer, the new surface color. The discolored plastics have been perfectly restored to the original color and match the housing well.

The housing didn't change color because it had been professionally painted by a WE refurb site using Polane. The paint was the exact color, a perfect match to the color that showed on the inside of the housing. A very nice match. Polane is a very hard, 2 part resin paint that does not change color over time and in this case it nicely shows how green a blue plastic phone can become over time.

( Clicking on the images below will enlarge them showing more detail than the thumbnails above )
« Last Edit: May 24, 2020, 01:42:32 PM by TelePlay »

Offline TelePlay

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Re: Practical plastic discoloration analysis
« Reply #2 on: January 13, 2020, 08:25:17 PM »
More on chemical treatment and application to clear plastics

( the following is the edited body of a second PM sent to another member who specifically asked, in a PM, about chemical treatment of clear plastics that had yellowed and more about the chemical treatment of plastics in general )

As for clear plastic which has yellowed, I don't think that either chemical treatment or surface removal (sanding) will work in that being clear, the UV light will have penetrated through the plastic making the yellowing pretty consistent all the way through the thickness of the plastic. The exterior surface may be more yellowed than the interior surface but the depth of yellowing from the exterior surface inward is unknown but probably substantial.

With colored plastics you can always look at the inside to see the original color and then from experience, the discolored layer is a very thin on the surface. UV light is stopped or blocked by the surface layer and that's where the chemical color change takes place.

I don't have any clear phones to check or test so if you have one that is yellowed, you might want to look at the inside of the discolored clear plastic to see if the inside looks lighter. That may be hard to do given that any yellowing will show through so it may be hard to tell what the inside really is. I would guess that the plastic is yellowed, to some extent, all the way through with the exterior surface being more yellowed than the interior surface - much of the UV light will have been used up at the exterior surface so less would make it to the middle and inside layer of the plastic.

My thoughts on the chemical treatment of discolored plastic is that it is only a band-aide. It's one of those things that seems to work but in reality the chemical treatment is the same as the process that changed the color, discolored the phone, in the first place, with the chemical treatment just creating a different color, hopefully closer to the original plastic color.

I'll try to explain color here. Color is created or generated in two ways: reflected and transmitted.

Transmitted is putting a colored gel in front of a lamp or painting a bulb in some way. The gel or paint is used to allow certain portions of white light to get through and what is passed through is the color seen or projected onto some object. For example, a gel or paint that absorbs only red light will produce blue light. If the gel absorbs red and blue light, that would produce a green light. The colored light is projected onto a surface to light it in some desired way (theater and stage lighting). This is not what is happening with plastic color change.

When someone looks at an object illuminated with  full spectrum "white" light, they see its color. The color seen is the result of the object absorbing some colors out of the white light spectrum and reflecting the rest. A phone that looks blue is absorbing red light and reflecting everything else. White plastic reflects all colors, all light, and a black items reflect virtually no colors, no light (That is why black surfaces heat up more than white surfaces when exposed to sun light. Black objects absorb most of the suns radiation, its light. White objects stay cooler in sun light because they reflects most of the white light spectrum, making them look white, and very little energy is absorbed by the object. As such, white objects stay cooler than black). A green object is absorbing red and blue and reflecting green light making it look green.

When an object is illuminated with full spectrum white light, the color we see is only the reflected light, the color(s) that are not absorbed by the object. An apple is red to our eyes because the apple skin absorbs green and blue light reflecting only red.

When the surface of a plastic is exposed to UV light, atmospheric components and chemicals including hand oils, cleaners, etc. that very thin layer of plastic at the surface can undergo molecular changes and that will change the properties of the plastic

The way a desired color is manufactured is by mixing different plastics with different reflective properties so that the final plastic only reflects the desired color. The white light wavelengths, colors, that are absorbed go into the plastic and are either harmlessly absorbed (with some minimal heat build up) or they can change the chemical bonding of the surface plastic molecules (UV light is highly energetic and is very good at breaking chemical bonds in the plastic at the surface - or deeper if starting with a clear plastic). The absorption of certain white light wavelengths, colors, takes place in the high orbital pi bonds of the molecules. The pi bonds are weak bonds which if exposed to just the right wavelength will resonate or "ring" and if enough energy is absorbed by the pi-bonds, they will break and the original wavelength (color) absorption and reflection properties of those pi bonds is changed, the surface becomes discolored.

This is a graphic representation of sigma (strong) and pi (weak) bonds

The C to C sigma bonds holding the plastic molecules together are strong, basically unbreakable unless plastic is totally destroyed. The pi bonds are high orbital, weak interactions of electrons well away from the C atom bonds and these are the bonds that are designed and created by chemists to absorb and reflect specific light frequencies causing the plastic to look a specific color. The pi bonds are quite weak and can be changed or broken by energy including UV light.

Once the surface molecules are changed, getting them back to "as made" is impossible but additional changes by further bonding destruction may produce acceptable results making the plastic's surface develop an absorption/reflection state that improves the discoloration. This is what is happens when using a bleach or peroxide process. Chemical treatment of the plastic's surface layer is really just further damaging or changing the already damaged or changed pi bonds and in some colors of plastic, it seems to work. Can bleach or peroxide turn the discolored plastic's pi bonds back to what they were when originally made? No. Chemicals can only make further changes in the bonds with hopes of those changes making the plastic "look" better for some period of time.

Take the AE orchid plastics. As made, they absorb yellow light leaving orchid, purple, to be reflected so the phone looks purple. As the pi bonds are broken, the plastic begins to absorb yellow and orange. That makes the plastic look blue. Starting with original blue plastic  which is absorbing orange, as it undergoes pi bond breakage it begins to absorb orange and red making the blue plastic reflect or seem green - blue 500's turn greenish over time as they discolor.

You can see in this reflective color wheel below how orchid is created in the plastic surface (absorbs yellow) and how it changes to blue when orange begins to be absorbed when the surface pi-bonds are damage.

And, it can also be the case that the plastic will just absorb more light across the white light spectrum causing the plastic to look darker along with showing a color change. Beige and green phones, for example, become darker as they change color. Both the darkening and color changes can take place at the same time. As such, this color change, discoloration over time, is quite complex.

Using chemicals to "cure/fix/restore" the color change is nothing more that messing with the plastic surface's pi orbital bonds that have already been messed with but by using an oxidizer at a much faster rate that the original discoloration that took place over decades. In that bleach and peroxide have been used to lighten or whiten clothes and hair, it's easier to see why a bleach or peroxide chemical treatment will work better on light colored phones and not on darker ones. It might also be why splotching is more prevalent on darker colors in that a slight change to a lighter phone's plastic won't show the splotching which would be much easier to see on a darker plastic.

For example, take an ivory housing which has turned darker. That means that the pi bonds have changed so they absorb more light and reflect less making the housing look about the same color but darker. The pi bonding change might also cause different wavelengths to be absorbed/reflected which would also change the perceived color. Lighter plastics from the start are reflecting a lot more light than a darker colored plastic so there is less to "improve" to lighten or slightly change the color with a chemical treatment than on a darker phone which is absorbing a lot of light and would tend to not respond as well as a lighter phone.

So, it would be easier for a bleach and peroxide, oxidizing agents that are known to make things look brighter and whiter, to have a better affect on lighter colored plastic, to reflect more of white light and not show splotching as easily as a dark plastic. Darker plastics, blue or red or brown, use massive light absorption to create the darker colors. An oxidizing surface treatment would more easily splotch those surfaces and possible result in an undesired overall color change. Trying to change a little bit on the surface of a lighter phone is most likely going to be more successful than trying to change any of the many color absorbing characteristics of a darker phone. Pink and yellow are in the middle with pink if not too discolored responding favorably to chemical treatment. I guess one could say that lighter plastics can be improved with bleach or peroxide but darker plastics could be made worse, damaged to the point of requiring sanding to remove the damaged layer to restore the phone's color.

The bleach or peroxide oxidizing chemical treatment is changing the molecular pi bonds on the phone's surface with the hopeful result being a change back to something that is close to the original color. With lighter colored plastics, this is usually the case depending on how badly the plastic had been discolored. How long will it last? That's an unknown. A pink WE 500 housing that I treated successfully with peroxide creme returned to its darker, salmon color after about 6 months of storage in a dark area. It seems the pi bonds affected by the peroxide reverted back to the salmon color all by themselves, whatever was changed by the peroxide was not permanent and the pi-bonds reverted back to their pre-treatment discolored properties.

The only definite statement that can be said about chemical treatment is that only sanding off discolored surface layer will restore the plastic to its original color. Yes, sanded plastic will change color just like the original surface layer had discolored over a very long time but the restored plastic might not change at all if the phone is not displayed in sunlight. Anyone who has sanded off a discolored surface layer knows that the side of the phone facing a window was usually more discolored that the side facing away from the window and areas under the handset and its cups were not as discolored as the areas surrounding those protected areas.

So, back to CLEAR plastics. None of the above really applies to them in that the yellowing, I think, goes much deeper than than the surface and chemical treatment of the surface will affect only the surface. There is no way to repair the pi-bonds in the plastic below the surface layer. Clear plastic contains no dyes or pigments and it most of light that hits it to pass through the plastic, and reflect light from internal parts back through the plastic, transparency. The original clear plastic look light or white as well. As UV light passes through the clear plastic, bonds within the plastic are changed and the plastic begins to absorb in the purple range of the white light spectrum making making the small amount of light that is reflected, that does not pass through the clear plastic, look yellow and possibly darker if the bonding changes also cause the plastic to absorb more light in general. Clear phones are  not invisible, they do reflect some of the white light that hits them so they can be seen. The absorption of purple out of that white light makes the clear plastic appear to become yellow.

And, finally, chemical treatment of the surface is just a band-aide. It is a brute force attach on the plastic surface molecules which is not a precise chemical reaction. It is doing further damage, not repairing, molecular color creating pi bonds in the plastic that were initially a specific mixture of pigments and dyes designed by the companies chemical engineers to create the plastic's original color. When first molded, the melted plastic was a will mixed combination of several colored plastic pellets to create the desired color after injected into a mold, cooled and removed from the mold. From that point on, the plastic surface was exposed to external agents and the discoloration began. Discoloration was the changing pi bonds of color creating molecules, damaging those molecules on the plastic's surface, and the use of a oxidizing chemical treatment on the damaged plastic does nothing more than further damage those color creating pi-bonds in hopes that the further damage will result in a color change that takes the discolored plastic back to something close to the color of the plastic when it was removed from its mold.  That oxidizing treatment reaction is unpredictable and the stability of anything changed by it is also not known. Chemically treated plastic could remain stable for years or it could change back, discolor again, in a few months at it did with the pink housing used in an example earlier in this topic.

I don't know if bleach or peroxide will change the plastic's physical properties to make it harder the way it has been seen on plastic housings that have been more than slightly discolored. Discoloration over time make the plastic's surface layer much harder than the original ABS. And since discoloration, and hardness, is greater on the side of the housing that had been facing sunlight for a long time, the physical properties of the surface plastic in the housing varies from area to area. I don't know if bleach or peroxide will penetrate the hardened surface layer in the same way it penetrates the lesser discolored and softer shielded areas. If the oxidizing process is affected by plastic hardness, then an overall exposure to an oxidizing agent will show different results on the hardened surface area than the softer plastics. The oxidizing agent seems to just affect the color of the plastic and does not make it harder the way years of exposure to high energy UV light did. The only question is how is the oxidizing agent working on harder surfaces versus softer surfaces on one specific discolored housing. It just makes sense that the harder plastic, the ABS that is resistant to pure acetone, would not the chemical reaction to penetrate the thin surface layer as well as on softer plastics. This would either create different results on different areas of the housing and if it only changes the surface of the discoloration would not be as stable of a color change that would be achieved on the softer plastic which allowed the oxidizing agent to get deeper into the surface layer. None of this is know but it does provide some food for thought when using chemical treatment.

One last thing about plastic hardening. I do know from experience, that discoloration of plastic also makes the plastic much harder than the original plastic. There is something going on with UV exposure besides breaking of pi-bonds which changes light absorption and reflective properties of the plastic but also changes the physical properties of the plastic. I've had colored ABS phones where pure acetone on a cotton cloth would not easily dissolve the hardened plastic surface. I would really have to rub hard and a long time to chemically sand off that hardened layer. Once it was gone, the acetone cut into the original plastic easily causing the cloth to "stick" or feel like a tack rag on the original plastic - and that way to know when the discolored plastic had been removed and I could move on to another area. What is causing the ABS to turn to solvent resistant, almost glass hard plastic is unknown.

Discoloration related hardness changes has a definite affect on surface removal with sandpaper. The moss green that I I restored had a hard dark green surface layer that did not want to sand off easily with 320 grit paper so I went down to 80 grit to cut through it. I found it took less time to use 80 grit and then sand that back up to 400 grit than it would to spend hours with 320 grit slowing working my way thought the hardened layer. 80 grit original ABS can be sanded up to 2000 grit in a few minutes, a lot shorter time than it would have taken to get the hardened layer off using 320 grit.

« Last Edit: January 24, 2020, 07:26:47 AM by TelePlay »

Offline Jim Stettler

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Re: Practical plastic discoloration analysis
« Reply #3 on: January 14, 2020, 01:04:13 AM »
To try out a variation of my new favorite quote from Jack Ryan:
You make it sound complex , but in reality it is much not near as simple as you make it  sound.

This is really good info. It takes more than 1 read to comprehend the chemistry basics for me . There is much more than basic info in this post.
Thanks for tackling the topic John. I really appreciate the clear perspective.

You live, You learn,
You die, you forget it all.

Offline HarrySmith

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Re: Practical plastic discoloration analysis
« Reply #4 on: January 14, 2020, 06:52:44 AM »
That is a lot of information. Thanks for posting it. That clearly anwers a lot of questions. I am not nearly finished digesting it so I am suire there are a lot more answers.
Harry Smith
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there is only
do or do not"

Offline Dan/Panther

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Re: Practical plastic discoloration analysis
« Reply #5 on: January 14, 2020, 01:17:45 PM »
Great post. That Blue Purple AE, Looks great in either color.


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Re: Practical plastic discoloration analysis
« Reply #6 on: January 17, 2020, 09:38:36 AM »
Color creation: The chemistry of colored plastics and why colors change

Reflected Light:

Everything one sees (not including projected light images, eg TV) is the result of light being reflected off of an object's surface. White light (e.g. full spectrum sun) hits the surface of an object and what happens to the light after that, how that light is reflected, determines the color and shade of the object. The illuminated surface is seen after selected wavelengths of the full white light spectrum are absorbed by the surface and the rest of the light is reflected from the surface. The combination of reflected light wavelengths created the color of the object. If almost all of the light is absorbed, the object looks black. If almost all of the light is reflected, the object looks white.

Between white and black, whatever light wavelengths are reflected determines the color of the object. Light is energy and the more light absorbed, the warmer the object becomes. A black car absorbing almost all of the sun light hitting it will get much warmer that a white car which reflects almost all of  in sunlight. Absorbed light energy increases the temperature of the object absorbing the light.

This image below is an example of white light (visible spectrum consists of wavelengths between infrared and ultraviolet) illuminating an object that has the ability to absorb all wavelengths except those that produce green. The light that is not absorbed is reflected and looks green to the eye. All colors are created this way, by selective absorption of the white light illuminating the object and reflecting the rest.

Molecular Bonding

Molecules exist by way of sigma bonds (atom to atom bonding) and pi bonds (higher orbital bonding). Sigma bonds vary from strong to weak with basic bonds being relatively strong within the molecule to weak in bonds used to attach chemical groups to a basic molecule. Pi high orbital bonds are “cloud” bonding by orbital electrons and are not as strong as sigma bonds. This is a simple representation of those two bonds.

Molecular Synthesis

Everything is made by connecting atoms to each other to build, to create molecules desired for some purpose. These molecules can then be combined by reaction with other molecules to get the desired chemical properties. These molecules can be quite large and complex. Molecules can then be mixed with other molecules to create a complex mixture and this is the case with phone plastics. The plastic (ABS for example) is mixed with dyes, pigments or plastic pellets, that have already been colored, in a proportion that creates or produces the desired color of plastic.

Chemical synthesis is basically putting two things together in a reaction. These molecules are made larger, and more complex, by breaking a weak bond in an existing base molecule and replacing the part broken off with another molecule that has a stronger bond affinity to the base molecule. This process can be done over and over until the final desired chemical, molecule, is achieved.

Phone plastics are a blend of the polymerized plastic molecules, which are generally off white by themselves, and complex color generating molecules. The color molecules, which can be pigments, dyes and/or colored plastic pellets, are mixed within the base plastic and are not part of the base plastic itself. The color creating molecules retain their physical properties when blended with the plastic to create the color of the plastic. The color creating molecules are complex and contain many cyclic rings and double pi bonds.


The color seen in plastic is the result of adding complex molecules that absorb certain, desired, wavelengths and reflect the complementary color to the plastic . This image below is that of a relatively simple "chromophore" or a color producing molecule called Tyrian purple. This molecule's pi-bonds absorbs light from the yellow part of the visible spectrum and reflects light from the red to blue part of the visible spectrum. That reflected lights is seen as violet (purple). Mixing this chemical or molecular chromophore, this compound, with a base plastic will result in a purple plastic.

Below is the molecular structure of two ABS (Acrylonitrile Butadiene Styrene) molecules connected to make a simple polymer. Note the lack of cyclic structures (1 per molecule) and double pi-bonds in comparison the the Tyrian purple chromophore above. The lack of complex pi-bonding means ABS has little if any ability to absorb light so most of the visible spectrum is reflected, it looks whitish or off white if not colored.

Phone plastic (ABS, etc) is a long chain polymer with many more than 2 molecules connected together. When chromophores (as many different ones as needed to get the desired color) are added to and blended well with melted ABS, injected into a mold, cooled and removed, the cast plastic part will have the color of the mixture of the chromophores added to the polymer.

Chromophores are created by chemical synthesis (adding stuff to stuff) to create a final molecule that reflects a specific color. They are complex molecules with a lot of cyclic rings and double pi-bonds. Below is an example of 4 chromophores that are quite similar in general but each is slightly different and that difference is which causes each of the chromophores absorb or subtract from the visible spectrum specific wavelengths which causes it to reflect a desired color, the color if each is shown superimposed on each molecule. Color discoloration occurs when any of those smaller molecules attached to the base molecule are split off by an external agent.

While sigma bonding is quite strong, the bonds used to attach shorter molecules to the cyclic (circular) chained molecules are weaker and these are the weaker bonds that can be broken by external agents and that "degradation" causes a change in the chromophore's absorption properties (which wavelengths will be absorbed resulting in a reflected light color change). The shorter molecules added to the cyclic structure are molecules intended to "tune" the chromophore's pi bonds of its double bonded cyclic molecules. The added molecules affect the electron flow (the electron cloud) of the pi-bonds either increasing or decreasing the light wavelength that will "ring" the bonds, to "tune" the molecular bonds, and have the chromophore absorb that "ringing" wavelength of light and reflect the rest of the light as the desired color. The high orbital pi-bonds that are responsible for absorbing selected wavelengths (specific to the designed chromophore molecule to create a specific color) and any change to the molecules pi bond "cloud" by splitting off a small segment of the chromophore will change the absorptive properties of the chromophore so that different wavelengths (colors) are absorbed and the light not absorbed is reflected as a different color - or discoloration.

Using the simple double bonded carbon molecule structure of ethylene, it shows 2 carbon atoms bonded together by a double bond, one of which is a sigma (carbon to carbon bond) and the other a pi (electron orbital) bond which has the electrons "flowing" from one atom to the other in a "cloud."

UV light is part of the energy spectrum from the sun but it is outside the visible spectrum so is invisible to the eye. It is high energy light not only penetrates the plastic surface but also can break bonds in the plastic's chromophores. UV light has enough energy to split off part of a chromophore and cause a the color of the plastic to change, to discolor the plastic. This is done by the UV light breaking the weakest bond of a chromophore splitting off a segment that had some affect on the pi-bond cloud to create the desired color. Removing one segment alters the pi bonding cloud which changes the light wavelengths that are absorbed. Changing what is absorbed changes what is reflected. Changes in reflected lights changes the perceived color of the plastic, discoloration is observed.

The UV energy "degrades" the molecular structure of a chromophore. That alters the absorption properties resulting in different wavelengths being reflected, the degraded chromophore reflects a different color, or discoloration. This example below shows what happens to a green chromophore when part of it is split off and its absorption/reflection characteristics change.

This example above shows UV light splitting off an amine (NH) molecule from a green chromophore. The split off molecule while attached affected the pi bonding cloud causing the chromophore reflect green. With the amine molecule gone, the chromophore's high orbital pi-bonding cloud changes and the properties of the changed "cloud" reflects brown.

Each chromophore has many double bonds which are a sigma and a pi bonds. The electrons of the pi bonding "cloud" are affected by electrons in the smaller segments attached to the basic chromophore. The addition or removal of parts of the chromophore affects the "cloud." A newly synthesized chromophore is balanced or stable and produces a specific color. The ability to absorb the desired wavelengths in the newly synthesized molecule will be changed if an external agent in some way changes the pi-bonding cloud of the molecule. Changing the structure of the chromophore by removing a part of it affects the "cloud" causing the "resonant" frequency of the pi bonding "cloud" to change. That changes which light wavelengths are absorbs and reflected.  or the original color becomes discolored. The plastic will begin to look discolored.

Since only some of the chromophores are degraded over time, the result is a mixture of the original chromophore color and the newly created (damaged) chromophore color in the plastic. The "new" color of degraded surface colors will be a combination of the original color and the new color being reflected by the damaged chromophore. The degredation of chromophores is a slow process and it will present a full range of "new" colors as the process continues over time.

With the number of different chromophores being very large, the plastics they are mixed into being proprietary to the manufacturer, the amount and type of plasticizers added, the external agents affecting the plastic, the temperature of plastic during interaction with external agents and the length of time exposed to agents (decades), it is not possible to predict what the color of any particular plastic part will look like over time.

Reflected Light Color Creation

While the following applies to everything, it will be directed toward plastic used to create phone parts. Colored plastics are produced by mixing dyes and pigments with molten plastic to create basic colors in pellet form. Colored pellets are mixed together in a ratio that would create the desired color for an object. The pellets mixture are melted and blended together stirring and then injected into a mold. If not fully mixed, a swirl patter is seen in the plastic. The final color of the object depends on which pellet colors were mixed together.

The dyes and pigments added to plastic to create color and are called chromophores which are light absorbing molecules. They are synthesized to selectively absorb certain wavelengths out of the full visible light spectrum. The wavelengths that are not absorbed are reflected from the surface. The mixture of reflected light wavelength (all not absorbed) produces the color of the object.

This complementary color wheel shows the colors that make up the visible white light spectrum. This is a complementary color wheel in that it shows if yellow is absorbed, the remaining light reflected is purple. Absorb red and green is seen. Absorb green and red is seen. In discoloration, if yellow is absorbed by the newly molded plastic, it looks like purple plastic. Over time, as the chromophores are damaged and they begin to absorb longer wavelengths toward orange, the the color of the reflected light will begin to look blue. The greater the chromophore degradation over time, the more blue the plastic will become (as in the AE orchid housing).

It seems as if almost all chromophore degradation makes the chromophore absorb toward the longer, less energetic infrared side of the visible light spectrum. For example, a blue phone (absorbs orange) will begin to absorb more of the color counter clockwise on the wheel, which is red, and causing the blue housing to begin to look green. Orchid changes to blue. Yellow changes to orange (the image below shows that change from yellow to orange(ish) and how areas that were exposed to more UV will be more changed than those not receiving the same amount of UV over time).

It may be the case where a damaged chromophore would begin to absorb higher energy wavelengths, toward the ultraviolet end of the spectrum, but I have not found that to be the case in plastic discoloration. If that is true, then the addition of smaller molecules to larger base chromophores would always make the base chromophore absorb higher wavelength light and any change to a synthesized chromophore would cause the wavelengths absorbed to be less energetic, move from the ultraviolet to the infrared part of the visible light spectrum. If so, a blue plastic (which is absorbing orange) would begin to look purple (begins to absorb yellow) and that is not seen. Blue always seems to discolor to green, yellow to orange and orchid to blue, etc.

Since a specific colored plastic most likely contains a mix of different chromophores to obtain the desired color, each chromophore will react differently to the external agent(s) causing the change. That would mean the damage would not be uniform across all of the chromophores in the plastic over time. Some will be changed more than others so the absorption properties of the "new" mixture of original and damaged chromophores will create a unique discolored plastic caused by the new mixture or blend of surface chromaphores. Discoloration of a plastic can not be predicted by a simple rule for each plastic housing. Each plastic will achieve its own "new" color and darkness over time.


All of this can be summarized into the fact that chemical treatment is nothing more that a fast reaction (hours vs decades) on the plastic's surface that in some way will change the surface chromophores responsible for the discoloration in a way that is similar to the way it was discolored in the first place. The treatment may also change undamaged surface chromophores making the plastic's color becoming more discolored and look worse than before the treatment. The forced changes can improve the discoloration or make it worse (seems lighter plastics are better treated that darker one). The oxidizing reaction is a broad brush approach and some areas of the plastic may react differently than others for a variety of reasons (the change may not be uniform causing splotches). The oxidation reaction "bleaches" surface chromophores and changes their absorption properties. And, being a brute force approach using an known oxidizing agent on an unknown layer of molecules, it is not possible to determine what will happen, how stable the changes will be, or if the changes will be temporary and "new" reverting back to some level of discoloration in a relatively short amount of time.

The only way to really change a discolored surface back to its original, uniform color is to remove the discolored, hardened layer by chemical or physical sanding (as in the yellow Accent housing and the blue WE 500 handset and bezel shown above). This returns the plastic back to its original color. That "new" surface layer will then becomes susceptible to change by external agents but over decades, not months or a few years. Chemical treatment may work in some way for some lighter colored plastics for some period of time but sanding off the thin discolored surface layer is the only way to get back to the original plastic color laying just under the discolored surface layer.

One final saving thought, while the chemical treatment does work to some extent on some plastic colors, if the treatment goes bad and the results are splotchy and/or a "different" unwanted discoloration appears, the plastic's original color can be recovered by simply removing the damaged surface layer by sanding, the ultimate fix.
« Last Edit: January 24, 2020, 08:08:20 AM by TelePlay »

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Re: Practical plastic discoloration analysis
« Reply #7 on: January 18, 2020, 01:17:00 AM »
Chemical Treatment Overview

The alternative to sanding (chemical or paper) to physically remove the top lay of discolored plastic is to treat the surface layer with a bleaching agents (bleach, peroxide or retro-brite which are all oxidizing agents) with the hopes of changing the chemistry of the surface layer so that the discoloration is removed, so the plastic looks it did when it first came out of its mold.

Discoloration is simply a changed or “defective” chromophore. The high orbital weak pi-bonds that do the absorbing and reflecting change due to UV light, innate chemical breakdown over time and/or environmental  agents (smoke, oils, cleaners and polishes) coming into contact with the surface. Over the life of the phone, the physical properties of the chromophores change which causes greater absorption of light (the surface becomes darker) and/or their wavelength absorption properties change causing the reflected “seen” color to change. An orchid housing is seen when the chromophores absorb yellow and reflecting all else. If the changed chromophore begins to absorb orange, the plastic will begin to look blue (AE orchid housing seemed to change quickly, and eventually completely by what seems to be the breakdown of what may have been not the most stable chromophores used when the orchid plastic was created).

The procedure of exposing a plastic to oxidizing chemicals (bleach, peroxide or retro-brite) to “fix” the discoloration is nothing more than causing a surface reaction that affects both the defective and good chromophores with the hopes of having the rather rapid chemical reaction change the plastic back into the color it was when molded.

“Bleaching” a plastic surface means exposing all of it to free radical oxygen atoms. The oxygen reacts with the chromophores in the plastic’s surface and changes, again, the chromophores which affects their absorption properties, to change which light that is reflected. This may result in seeing more or less light reflected and/or a change in the color of light that is reflected. It is an uncontrolled reaction in that no one knows what damage was done to the chromophores to cause the discoloration in the first place or what affect a bleaching agent will have on the discolored and remaining originally colored surface molecule of the plastic. By definition, the use of oxygen, or using an oxidation process, on the plastic “bleaches” the so it makes sense that chemical treatment of some (lighter) colored plastics will seem to work. And, the same chemical treatment could make other (darker) colored plastics worse. Oxidation seems to work to some extent on white, beige, yellow and pink. If defective chromophores result in a darkening of the plastic (absorbing a greater amount of light), oxidizing should work to make the plastic look lighter by decreasing the chromophores ability to absorb light and thereby make the plastic look lighter, more light is reflected. At best, it’s a trial and error, hope for the best process with the unknown being how long will the further changed chromophores be stable until they begin to change again and revert back to a discolored state.

Bleach is a liquid which is mixed with a enough water to obtain the desired concentration and be able to submerge the housing in it. This means that the bleach will oxidize both the exterior and interior of the plastic parts.

Hydrogen peroxide is a liquid which breaks down quickly once the bottle is open but the hair salon industry has managed to turn it into a stable, easy to work with creme that has a shelf life of several months after opening. This Volume Developer creme sticks to the plastic surface, does not run off, and can be easily used within a plastic bag which allows a little to go a long way.  The developers are available in Volume 20, 30, 40 and 50 which are increasing concentrations of peroxide. This topic reply

explains volume concentrations. While that particular topic started as a "what polish to use" discussion, it turned into the chemical treatment of discolored plastic in this reply to the topic end.


There is a lot of information posted on the forum from 2009 to about 2018 about oxidizing treatments to remove discoloration using either bleach or peroxide (hair salon developer or the retro-brite formula) as the oxidizing agents.

Chemical treatment is a broad brush, brute force approach or process that uses oxygen in a chemical reaction on the plastic’s surface which, if it works, will hopefully change the discolored surface plastic back to something close to the original plastic color. The intent with an oxidizing, chemical treatment is to quickly reverse years of slow color change due to a variety of external agents. The procedure is not an exact science and its variations include, but are not limited to, which oxidizing agent is used, how it is used, the molecular make up of the plastic, the cleanliness of the plastic surface that it is being used on and the dyes and pigments (original and changed) within the discolored plastic.

Given the number of phones that were produced, it’s safe to say that no two pieces of plastic found these days came from the same batch. The housing and handset on one specific phone probably came from a different mold pouring of mixed, blended or compounded plastic. Each mixture will respond to chemical oxidizing treatment differently. Over time, the plastics were exposed to different change agents so the discoloration itself is different for each plastic. Bonds are broken by way of any or all external agent processes mentioned above and when they break, the color changes. What the color changes to depends on the chromophore affected, which of its bonds are broken or re-arranged and the length of the time over which the bonding degradation took place.

There is no way to put the chromophores back together again as they were in the plastic as it came out of the mold. The only thing that can be done with an oxidizing treatment is to further change the plastic's surface chromophores to hopefully make the surface color look more like it did in the original plastic.

« Last Edit: January 24, 2020, 08:36:30 AM by TelePlay »

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This topic was created by using the content of several PMs to different people and several different topic ideas. There may be some overlap and duplication throughout the topic. It's intent is to be a primer for anyone interested in learning the basics of color and the chemical treatment of a plastic. If anything is in error, please feel free to correct it in a detailed reply.
« Last Edit: February 11, 2020, 09:51:13 PM by TelePlay »

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How to create a Chromophore:

     or, Organic Synthesis - building a complex molecule one step at a time

The question was asked if oxidation can restore damaged chromophores. The example cited in a reply above using a green chromophore being damaged by UV light

cannot be reversed by using bleach or peroxide in a one step surface oxidation treatment. In fact, it is impossible for any reaction to restore the damage done to that green chromophore, or any other damaged color creating molecule/chromophore.

When the UV light broke the bond in the middle of the green chromophore splitting of the attached Nitrogen atom and all that was attached to the other side of the Nitrogen atom, the high orbital pi bonding pattern of the “green” chromophore was disrupted and the new high orbital pi bonding pattern of the remaining chromophore produced or created an orange-ish color, the UV created discoloration.

To undo this splitting, to make the “discolored” orange chromophore produce green again, the Nitrogen atom of the split off molecule would have to be reattached to the once green chromophore exactly as it was before being split off.

This cannot be done with peroxide, bleach or any other highly sophisticated organic synthesis reactions. The following is what the oxygen from peroxide or bleach would have to do the “restore” the true color, turn it from orange to green in this case.

1)  The double bond in the damaged chromophore would have to be broken allowing half of the bond to keep the chromophore together and making the other half available to and looking for something to attach to
2)  One of the Hydrogen atoms on the chemically neutral NH2 part of the split off molecule would have to be removed to create a -1 negative NH ion molecule “looking” for a place to bond
3)   The available bonding link created in (1) would have to find the Nitrogen ion created in (2) to recreate the single bond that once held that Nitrogen molecule to the chromophore.

If the 3 steps above could be accomplished by simply throwing a lot of Oxygen atoms at the discolored plastic reversing the UV damage, then the original chromophore would exist and then it would once again produce green reflected light. This is not possible in a one step radical oxygen ion treatment. The green chromophore was created in a step by step organic chemistry synthesis starting with a simple C=C Ethene or Ethylene  molecule or pure benzene.

Other colors would be damaged differently and would require different "reconstitution" steps to return them to their true color.

The following synthesis map shows how pure benzene can, in only 3 separate chemical reactions, be transformed into Phenol. To do so, pure Benzene (green box) first undergoes a Friedel-Crafts Reaction (4) to create an aromatic ketone (ketones are a class of chemicals defined by its chemical structure) by replacing one hydrogen atom on the benzene ring with the ketone structure. Then, a Baeyer-Villiger Oxidation (16) reaction is used to convert the ketone to an ester (ester is another class of chemicals defined by their structure). The ester then undergoes Ester Hydrolysis using water and lye (sodium hydroxide) to produce Phenol, a molecule consisting of a benzene ring with one OH molecule attached to it. Phenol is a widely used chemical for many things from antiseptics to the part of becoming a phenol-formaldehyde resins (requiring additional steps to create the "mixture") which are used in PC boards and other places where electrical conductivity is not wanted. And, as we all know, phenolic resins are a type of synthetic thermosetting resin invented by Dr. Leo Baekeland in 1907. The material was originally called Bakelite and was effectively the first plastic to be sold commercially. So, getting from Benzene to Phenol to then create Bakelite is more than a one step chemical synthesis process.

The green chromophore in the example above was created by going through at least 20 individual and highly specific chemical reactions. Each reaction is designed to have an molecule to be attached attack and cleave a part of the base molecule so it can attach itself to the base molecule, add a building block to the molecule under construction. The green chromophore was “built” one step at a time starting with a simple C=C molecule or benzene. This is the “road map” for breaking (cleaving) bonds of Benzene and related aromatic hydrocarbons so that “other’ molecules can be attached to the cleaved point to “build” toward the final desired product (chemical), step by step.

(full sized image attached to this reply:

And this is the organic chemistry road map dealing with cleaving and bonding (systhesis) of Alkanes, Alkyl Halides, Alkenes and Alkynes (non-aromatic molecules). Aromatic molecules are those that have a ring structure such as benzene (6 carbon ring), cyclo-pentane(5 carbon ring), heptane(7 carbon ring) etc. chemicals which by definition produce aromatic odors.

(full sized image attached to this reply:

Looking at the maps above, one can see almost anything can be "created" starting with C=C or Benzene. By taking many steps using specific chemical reactions, one can add “stuff” on to a benzene ring and then add “stuff” onto that newly added "stuff" and so on until the highly complex molecule desired, such as the green chromophore, is created. The circled numbers in the maps refer to the specific chemical reactions listed next to each map (and any names shown are the chemists who first discovered that specific reaction, and had the honor of having it named after them).

To answer the question "can color be restored with peroxide or bleach," the answer is NO. There is no reaction in the road maps above, or any of the 5 or 6 other road maps dealing with other basic chemical groups of molecules, that would reattach the split off Nitrogen molecule to the discolored Orange chromophore to make it Green once again. And even thinking this could be done in a hardened plastic polymer (not in a liquid state) is folly. Oxidation treatments, bleach or peroxide, only further attack chemical bonds on the plastic’s surface creating different degraded chromophores, some of which can seem to show a perceived “improvement” in discoloration (in light colors usually) but peroxide/bleach can in no way ever recreate the original chromophore which is, as originally created, just below the discolored surface.

Removal of discoloration by paper or chemical sanding is the only way to restore a discolored plastic to it’s “as built” original, true color. Sanding is true color restoration work which will expose the original true colored plastic just below the discolored plastic surface layer. The true color of the plastic, just below the discolored layer, is the same color that is seen on the inside of a phone housing or handset, areas not exposed to UV light and other discoloration agents over decades of the phones life.
There are no chemical short cut, quick fix reactions that will ever change discolored plastic back into its true, original color.
« Last Edit: February 12, 2020, 08:18:24 AM by TelePlay »

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 The Chemistry of Color: A Chromophore and its Variations

It doesn’t take much of a change in a chemical structure of a complex molecule to alter its light absorbing/reflecting properties. A chromophore can be described as the section of a molecule will have alternating double bond and/or conjugated double bond which causes us to see color. The chromophore section will absorb some light wavelengths and reflect the rest thereby creating a color unique to a specific chromophore molecule.

The following chart starts with a molecule (1) which has a complex molecular structure but it is not a chromophore, it does not create/generate/produce a color. But, by putting that molecule through 3 simple chemical reactions, it becomes a chromophore that looks green, reflects green light and absorbs the rest.

The first reaction is Cyclization which breaks the Oxygen double bond, adds a Hydrogen atom onto the Oxygen atom and uses the other half of that bond to attach the adjacent Nitrogen atom by way of a single bond. That results in a 5 atom ring with 3 Carbon atoms (not shown) and 2 Nitrogen atoms (red circle and red line). That is molecule (2) in the above chart.

The next step is to Dehydrate the molecule by stripping of the –OH molecule and one Hydrogen atom attached to the adjacent Nitrogen atom (which are released as H20 or water, the waste product of that reaction) and creating a double pi-bond between the Nitrogen atom that lost its Hydrogen atom and the adjacent Carbon atom (green circle and green line). That is molecule (3) in the above chart.

The third step is to oxidize the molecule using pure oxygen to cleave, or splits off, 2 Hydrogen atoms attached to 2 Carbon atoms (inside the blue circle) which as hydrogen ions attach to an free ionized oxygen molecule to peroxide, the waste product of the reaction. The result is to create a double bond between the 2 Carbon atoms which turns the molecule into a green chromophore. That is molecule (4) in the above chart.

The Oxygen will only attack that specific Carbon to Carbon bond because it is the weakest Carbon to Carbon bond in the entire molecule (all other Carbon to Carbon bonds are adjacent to another double bond or another molecule; this is known as one of the rules of organic chemical synthesis; if there were two pure Carbon to Carbon bonds in the molecule, both would be converted from a single bond to a double bond and the molecule would have different properties).

One additional example of how easy it is to change a chromophore, to experience discolorations, it to take the green chromophore (4) and remove the Hydrogen atom attached to the Nitrogen atom (in the blue circle). Doing so creates a double pi bond between the Nitrogen atom and the Carbon atom is was attached to and that one very small change alters the chromophore’s properties from green to red, molecule (5) in the above chart.

The red chromophore can be slightly altered to produce a pink, yellow or orange chromophore. The green chromophore can be slightly altered to a brown, blue or purple chromophore. Compare the molecular structures of each to see the differences.

While these chromophores can be synthesized in the lab or chemical factory, many of them are synthesized naturally, created by plants, and can be chemically extracted for use with other materials. Letting a living plant do all the hard lab work is a lot easier than bench top synthesis. However, a plant synthesized chromophore is easily altered to create a different, custom color on the bench top.

This shows the complexity of a chromophore and the ability to change it’s color generating properties by doing something as simple as converting one single bond to a double bond. UV light, and other surface discoloration agents, can change the molecular structure of some of the chromophores in plastic with the only known result being perceived discoloration. Exactly which bonds were broken that altered the color, caused the discoloration, cannot be known and the ability to fix those damaged molecules in the plastic’s surface layer, to make it as it once was with anything including bleach or peroxide, is just not possible.

Brute force surface oxidation, chemical treatment with bleach or peroxide, cannot and is not going to restore the chromophore and get the discolored plastic back to its true, original color. It doesn't take much to damage a chromophore, just break one random bond in the molecule, and end up with discoloration. But, it is an impossible task to repair the damage once done.

While bleach or peroxide may make a discolored, lighter colored, plastic look better, it is not repairing the damaged chromophore. It is doing something else to the existing chromophores, damaged and original, the produces a perceived improvement in the discoloration. Removal of the discolored surface layer is the only way to get the plastic back to its original, true color.

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Light Sources: The other part of color generation

The "other" aspect to perceived color deals with the light source itself. The first image below shows the visible light spectrum from several sources. The top spectrum is daylight, or sun light, and is continuous from ultraviolet (blue) to infrared (red). The intensity drops off on the infrared end due to the long "warming" wavelengths being absorbed by the atmosphere.

It is the infrared part of the spectrum which provides the warmth this planet needs for life to exist. In the second image below, the electromagnetic spectrum to the right of Infrared shows the longer wavelengths moving from heat (infrared) to microwave (including cell phones) to radio (AM and then FM) wavelengths to the ELF (extremely low frequency) radio waves use to communicate with submarines well below the ocean surface.

At the other end of the sun's spectrum are the high energy short UV wavelengths which cause damage from sunburns/eye damage/skin cancer to the discoloration of plastic. While the blue end of the spectrum is needed to provide color, it is the ultra-violet, high energy wavelengths shorter than 400nm that can not be seen which cause damage. From the second image below, it can be seen that the spectrum moves from UV to X-ray to Gamma rays, all of which can damage things.

Back to the visible part of the electromagnetic spectrum, this is the light used to "see" everything. The light source illuminates an object and whatever wavelengths are not absorbed by the object are reflected as the object's color. Using full spectrum sun light, the reflected "color" is the most accurate representation of the objects color based on what chromophores were added to the object during production, what was intended by the manufacturer to be seen. I would assume they mixed their pigments and dyes to produce a desired color in universally available sunlight and its closest artificial source, light generated by the tungsten filament Edison light bulb.

Given any of the light sources in the first image below, it can be seen that as the source changes from sunlight or tungsten (heat) generated light, the continuous visible spectrum from the artificial sources begins to break down, some wavelengths or colors are missing in the lighting source and the intensities of spectral ranges vary.

The incandescent Edison bulb creates light by super-heating a tungsten filament in a vacuum. This produces little UV and less blue than the sun and being a light generated from a hot wire, it produces a lot more red and infrared that the sun (partly due to not having to penetrate miles of moist, infrared absorbing atmosphere. The visible spectrum produced by an incandescent bulb is continuous, it has no missing colors, making it very similar to sunlight.

LEDs can be found with different color or "warmth" levels from 5000K, considered to be daylight, to 2700K called "warm" light. The 5000K bulbs are made to emit a lot more "blue" light that the 2700K version and as such, the light from a 5000K bulb looks "cooler" or closer to the white light from the sun. While the LED bulbs produce a continuous spectral output, the intensity at different wavelengths can make a color object illuminated by them look different that the object if it were in direct sunlight. An object illumined by 5000K will look "bluer" or colder and an object illuminated by 2700K will look more "yellow" or warmer.

The CFL is the worse light source of all in that generates light in 5 or 6 narrow parts of the visible spectrum meaning many "colors" within the full visible spectrum are not present. This causes problem when a chromophore in an object is made to reflect any of the missing colors. If the color to be reflected by a chromophore is not there, the object will look discolored under the CFL source even though it is not actually discolored.

In order of color quality, after the sun, the incandescent was best, the 2700K LED next and the CFL last.

These light sources play a big role in color photography using digital cameras. After the light source and how the object looks to the naked eye, the quality of the camera, its lens and light sensor, can affect the photo being taken. Then, the camera's "software" that processes the image affects the "saved" image. Cameras try to adjust the image captured by the sensor to make it look "normal" and many times the adjustment can make the photo color look worse. I've seen my cameras produce different object colors based on the color of the surface behind the object, the camera "averages" out the image based on the white or gray background and in doing so, throws off the color of the object. I have yet to find the setting on my camera that tells it to just take the picture as seen in the view finder, to not process it when saving it from sensor to memory. My 12MP camera does not let me opt out of image processing.

The impact of all this on images is shown in the third image below. Using the recently color restored WE 500 moss green housing on an off-white background, the camera was set on a tripod (the timer was used for each picture to eliminate any camera movement blur), a reflector lamp was placed about 2 feet from the housing. The only change from image to image was the type of light bulb used in the reflector lamp. The images are notated to show the light source.

The tungsten image is the closest to actual except for the use of one 60 watt bulb which was less than one would use to take such a photo. A larger wattage would have produced a better image. The difference between the 5000K "bluer" LED and the 2700K "warmer" sources is noticeable. The CFL produced the largest image discoloration.

The interesting image was that taken under a red light. I would have expected the green housing to show dark grey to black in that all of the red light illuminating the green house should be adsorbed. If it were white instead of red light source, the housing would have reflect all other wavelengths making the housing look green. The image in the camera view finder looked dark grey but when the images was taken, it was processed by the camera to "make it look normal" and in doing so, the everything red image appears. The image was taken several times and it came out the same each time. And, each time, it took a few seconds to get from snapping the shutter to having the camera fully save the image to memory. It seems the camera, it all its programmed digital wisdom, noticed a low light situation and opened up the aperture to something it felt was large enough to capture a sufficient amount of light to make the image "look normal."

And then there is how a computer or smart phone or whatever will display a posted image, another variable to deal with.

Looking at the resolution of the color bulb images, the green/yellow/blue images all show similar clarity or sharpness (looking at the 714 area code). Only the color is off for each color. All off these colored bulbs have some amounts of green in their generated color and green is reflected from the green housing. As such, those 3 colors produced enough reflected light of off the housing for the "smart" camera to take a decent image. It was only the red bulb, which contains very little green, that caused the camera to open the aperture and take a blurred image. If that photo could have been taken as seen in the view finder, the housing would have been dark gray to black.

With respect to evaluating plastic discoloration, it is important to view the plastic under a good light source to see its actual discoloration and not its discoloration enhanced by a poor light source.

( click the images to enlarge them for better viewing )
« Last Edit: February 16, 2020, 11:47:32 AM by TelePlay »

Offline Jim Stettler

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I have read the best light color to use (from a conservation standpoint) is a matching color, Red light on a red object, green light on a green object ect. This is to reduce light damage to the object.
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Offline TelePlay

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With respect to light sources and "smart cameras" that out-think themselves, these are images of a WE 554 discolored yellow housing that was cleaned with mild soap and photographed at one time: same light source (equal mix of 5000 and 2700 K LEDs), same distance from the housing to the iPhone (about 20") and the same background (off white bed sheet).

The software in the smart phone tried to balance the colors it perceived and come up with a true to life color image. Didn't quite do it since the housing color as seen with the eye is actually between the lemon yellow left images and the and the brown beige right images. The housing is actually a discolored darker yellow, not beige.

In this composite image, you can see what the smart iPhone camera did to the white/grey background (off white bed sheet). The greater the area percentage of yellow plastic, the more blue the background. The less area percentage of yellow plastic, the more reddish the background. The software sees yellow and off white but does not come up with a good quality color captured image.

If there is a way to turn off the camera processing software in an iPhone and a Nikon 12MP camera, that is something I could use. Hard to take images of discoloration and true colors when the camera fights the process.

Offline TelePlay

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If there is a way to turn off the camera processing software in an iPhone and a Nikon 12MP camera, that is something I could use. Hard to take images of discoloration and true colors when the camera fights the process.

Doing a google brought me to the HDR setting on an iPhone. The High Dynamic Range function in the iPhone camera "blends the best part of three separate exposures into a single photo. Disabling that function results in a "raw" image capture. Below is the same sequence of photos with the only difference being the HDR function was not active. This is quite close to the sunlight color of the housing, but, taken with LEDs it is not quite the current true discoloration. Note the background being uniform from image to image.


EDIT:  For anyone interested in capturing the correct color, I was able to achieve the same results as above, if not a bit better, using my Nikon 12MP camera and setting the manual WhiteBalance setting to match the light source. This is pretty close to what the housing looks like in bright, natural light.

The first image is from an iPhone, the second from the Nikon camera.
« Last Edit: March 03, 2020, 12:39:43 PM by TelePlay »