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Chemical sanding method that will remove discolored plastic from a bezel

Started by TelePlay, April 08, 2018, 01:39:12 PM

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This topic covers the use of chemical sanding to remove discolored plastic from a bezel.

Since the bezel is the most complex and difficult part of a phone to chemically sand, this is a good place to point out a few things about chemical sanding in general.

Chemical sanding can provide "Oh, No!" moments. Since each plastic part is from a different factory batch with different colors, each part chemically sanded will react in a similar way but not exactly the same to solvents. The good news is that every "Oh, No!" moment can be easily and 100% recovered from by understanding what is going on and which step or individual technique can be used to resolve the problem encountered.

I had one of those moments the first time I chemically sanded an ABS bezel, an aqua blue. The horror was seeing the black plastic from the letter smear over the blue plastic. Just didn't think of that. The ultimate solution to that "Oh, No!" was found after trying a few things and is now part of the below procedure. Other "Oh, No!" moments are usually chemical sanding marks which are always easily and quickly fixed with wet sanding as shown in the scratch removal topic.

The intent of these chemical sanding topics is to present a general framework of how it's done. Given that, those who want to try it will be both successful at chemical sanding and learn how to fully recover from any "Oh, No!" issue. In fact, the procedures for all chemical sanding topics were created by finding fixes to more than a few "Oh, No!" moments and incorporating them into the procedures.

An example of modifying the procedures on the fly to get the best outcome occurred with this bezel. The first was, after noticing that the denatured alcohol left a light spot in the plastic test, the sanding ABS sanding solvent (acetone) was diluted to 75% with denatured alcohol to reduce the cutting affect of the pure acetone. If pure acetone were used, it may have been too aggressive in removing the top, thin, discolored plastic layer. Another on the fly change could be to change the final ABS solvent mixture from 5% acetone, 5% methyl ethyl ketone and 90% denatured alcohol to 10%-10%-80% to increase the cutting power might provide quicker results. Looking at the surface as the solvent or solvent mixture is being used is a good way to determine if it needs to be stronger or weaker for the best results.

This beige bezel presented 3 "Oh, No!" moments at the end of what was to me a canned procedure. The first was that the bezel was too shiny. It was recently mentioned on the forum that a correct bezel finish is not glossy but a more satin finish so the numbers can be more easily seen, not like reading letters on a mirror. The two other issues were minor chemical sanding marks that could only be seen in the gloss surface and three areas of minute black and beige plastic smear.

All three issues were resolved quickly by going back to 1000 grit wet sandpaper. This removed the sanding marks, the shine and it removed the last of the smearing. When rinsing and drying the surface after using the 1000 grit, it was easy to see the quality of the surface in that the low areas left by chemical sanding were still shiny. Once those areas were sanded dull, the surface was even, was smoothed by using the 5-5-90 solvent mixture on a soft cotton swab and then wet sanded with 2000 grit paper. After rinsing and drying the 2000 grit surface, the surface was chemically sanded with the 5-5-90 solvent on a cotton swab, a bit of Novus 2 was spread over the solvent damp surface and worked in with the last used cotton swap with a bit more solvent mixture. When the Novus began to get thick, the surface was wiped off with a clean, dry microfiber cloth. No buffer was used. Those modifications gave the surface was a smooth, satin finish and the numbers could easily be seen. the three "Oh, No!" issues were fixed with slight changes to the procedure ending with a very nice, original colored bezel.

With that said, on to the procedure to chemically sand a bezel to remove discolored plastic and leave it with a satin finish.


The bezel, removed from the dial, is best worked on by holding it in the palm of a hand. For the video, it had to be laid on a flat area which made work a bit more difficult and longer than it should have been.

First step is to test the plastics (beige and black) to make sure the right solvents are used in chemical sanding. On the back of the bezel, a small drop of denatured alcohol was placed on the beige and black plastics and let dry. Neither drops melted the plastic, This test indicated both plastics were ABS. If the bezel were Tenite or soft plastic, denatured alcohol would have melted the plastic. Acetone is used as the sanding solvent for ABS and denatured alcohol is used for Tenite or soft plastic. Now, since the alcohol left a light ring on the beige plastic, it was decided that the sanding solvent for the bezel would be diluted acetone to reduce its cutting power. The sanding solution would be 75% acetone and 25% denatured alcohol. If the bezel were Tenite or soft plastic, the sanding solvent would have been denatured alcohol and the final solvent would have been 30% denatured alcohol and 70% distilled water.

ABS was confirmed by placing a small drop of acetone on the beige and black plastic and letting it dry normally. Both drops left a distinct melt ring on the plastic, as expected.

The first step is to use a high bite cloth patch backed by a cotton ball and soaked with the 75-25 mixture to chemically sand off the discolored plastic. The swab is worked with pressure evenly over the bezel. Do not allow the solvent to pool on the surface and never stop moving with the swab in contact with the surface. The swab will fill with dissolved plastic so it must be change to a new, clean swab as needed. During this step, some of the black number plastic smeared onto the beige and the beige plastic covered some of the black lettering. This is not a problem. The plastic surface mixing will be cleaned up in late steps.

When all of the discolored plastic is removed, go over the bezel one last time with a clean swab and the 75-25 solvent mixture to both clean the surface and to smooth out chemical sanding marks.

The next step is to use a soft cotton patch backed by a cotton ball and soaked with the 5-5-90 solvent mixture. Go over the entire bezel with heavy pressure and evenly to further smooth the surface.

When done, place two pea sized amounts of powdered Rottenstone (Tripoli buffing compound) on the bezel. Use the last soft cotton swab well soaked with the 5-5-90 solvent mixture to pick up the Rottenstone on the swab and rub with pressure over the entire bezel and concentrating on the bezel areas that had smeared black plastic or black letters covered with beige plastic. The Rottenstone adds more bite to the final solvent. Add more solvent if the Rottenstone on the bezel begins to dry out. Do this until the smeared plastics seems to be removed. Then use a clean soft cotton swab with the 5-5-90 mixture to clean the compound off of the bezel and further smooth the surface.

Rinse and dry the bezel and look for sanding marks and smeared plastic. If any, they will be removed in the next step.

Use 2000 grit wet sandpaper to remove any remaining sanding marks and smeared plastic. If the smeared plastic is stubborn, drop down to 1000 grit wet sandpaper and concentrate on the smears. When to observed smears are gone, go back to the 2000 grit wet sandpaper using a random motion to evenly smooth the entire surface to 2000 grit.

Rinse and dry the bezel. Then use a soft cotton patch backed by a cotton ball and the 5-5-90 solvent mixture to chemically sand off the high marks left by the 2000 grit sandpaper. When done, and while the surface is still damp with the solvent, add some Novus 2 and spread it around evenly with a finger tip. With the last cotton swab used and a bit more solvent, rub the Novus 2 into the surface with medium to heavy pressure.

When the Novus 2 begins to get thick, add more Novus 2, spread it around evenly with a finger tip and use a rotating orbital buffer to remove the Novus and polish the surface.

At this point, the surface should be free of chemical sanding marks, smeared plastic, have a highly polished shine and no discolored plastic. If that highly polished shine is what is wanted, the procedure is finished. If marks, smeared plastic or discoloration can be seen, go back to the appropriate step to remove the issue and move forward to the final polishing step.

At the end of this video

it is noted that the highly polished bezel had the three "Oh, No!" issues stated above. The video ends saying how the issues were resolved - going back to 1000 grit set sandpaper and moving forward but ending without using a buffer to leave the surface in a even, satin condition.

As stated above, the important aspect of chemical sanding for either scratch removal or removing discolored plastic is to practice to learn how it works so that any "Oh, No!" that comes up can be quickly resolved with any of the step techniques used in each procedure. The key part is using the correct solvents for the plastic at an appropriate strength with the proper cloth swabs. Wet sandpaper from 600 to 1000 will quickly remove problems when chemical sanding is used between grits to remove high sanding marks and to keep the plastic in a "soft" mode.

The bezel, due to its shape, size and two colors, makes it the hardest of all phone parts to work on. Whether it is taken to a highly polished shine or left with a satin finish is a restorer's choice. Either way, chemical sanding to remove discolored plastic works. Below are the plastic test images and the before and after bezel images.


Thanks for the experimentation and the detailed process. I am going to try this on the next one I have to restore. Thanks for all the effort!
Harry Smith
ATCA 4434

"There is no try,
there is only
do or do not"


This will save me lots of time and "oh no" moments for sure. Last color set that was faded I worked on I ended up wet sanding it all by hand after melting a small spot... OH NO!  ;D Took forever by hand...
Thanks John