Sanding and Solvent Polishing WECo Hard Plastic

[cihensley@aol.com]

This is a continuation of posts in: http://www.classicrotaryphones.com/forum/index.php?topic=5239.0  Bill correctly pointed out to me that the previous thread had changed from crack repair to solvent polishing, and therefore warranted a separate thread.

In this next test I am using a badly discolored white handset. My intention is to remove all discoloration with MEK (using rags and a natural bristle brush). I anticipate that this will leave wiping marks in the plastic. I do not believe that MEK dipping alone will fully remove the wipe mark. This is borne out by Bill's cited experience.
I will sand the handset with 1500,1800 and 2400 grit micro-mesh paper. This is roughly the same as going up to 800 grit with regular sandpaper. Then I will then dip the handset in MEK to see if it eliminates the sanding scratches. The whole purpose of the test is to determine how much sanding can be reduced through the use of MEK.

Chuck

[cihensley@aol.com]

Here is the handset with the discoloration remove with rags and a brush soaked in MEK. The dirt marks came from the rubber gloves I had used before for other purposes. I will use clean or new gloves in the future. I masked out the embossing with Blu-tack so it was not obliterated by the cleaning. Total time spent was about 10 minutes. Minimizing the wipe marks would require longer, more careful cleaning, which is not an objective in this test. Now, to determine the amount of micr-mesh sanding required.

Chuck

[cihensley@aol.com]

I have not finished sanding the handset, but here are some preliminary observations. MEK removed all of the discoloration in about 10 minutes. Quick. It is taking longer to remove (by sanding) the rag and brush marks than if the handset discoloration was removed by sanding alone. Sanding allows more precise control (sharp edges, etc.) than MEK discoloration removal. There may be a role to for MEK in the discoloration removal of the grove around the holes in the transmitter cap and the concave receiver cap. Both of these areas are hard to sand. But the MEK removal must be carefully done to minimize removal marks. I think MEK will really shine in the final polishing.

Chuck

[cihensley@aol.com]

Here is the handset ready for MEK dipping. I had to go to 220 grit to remove the rag and brush marks. The right side (transmitter end) of the rubber band on the handset is sanded to 2400 grit micro-mesh. The left side is sanded to 12000 grit micro-mesh. Both caps are sanded to 2400. One of the purposes of the test is to determine if the MEK dip compensates for less sanding. I did not try to remove any of the discoloration from the embossing. I want to see the effect, if any, of the MEK dip on the embossing. I will do the dipping in two parts. First, I will dip one-half. Let it dry, then dip the other half. If there is no demarcation line I will not have to use a taller container on future restorations.

Chuck

[cihensley@aol.com]

Here are the first results from MEK dipping.

When it works well, the finish - sheen, depth and smoothness - produced by MEK rivals NOS. I have not been able to obtain the same quality of finish by polishing alone after micro-mesh sanding. A visible demarcation line was not apparent from doing the dipping in two stages rather than one (which would require a taller container). There was no improvement in the finish over the part sanded to 12000 grit versus 2400 grit. The MEK eliminated any sanding marks remaining after stopping at 2400. In fact, the crazing (which remains unexplained) was more predominant in the area sanded to 12000 grit.

I don't know yet what caused the crazing on some parts of the handset. All items were dipped the same (timing). The receiver cap , sanded to 2400 grit came out as desired. The transmitter cap also sanded to 2400 grit came out all crazed. All items were cleaned with denatured alcohol before dipping. This should have removed any surface contamination? But, I did not handle the parts with latex gloves which I will do in future tests. Where crazing occurred, it was on the exterior surface only. The reverse side (interior) was not crazed. What is affecting part of the exterior surface? The logo was not harmed by the dipping.

I plan to re-sand the crazed parts and try again. i will appreciate any suggestions or comments.

Chuck

[HarrySmith]

Nice results. Thanks for keeping us up on the results and the process. The crazing looks like what I got on my first retrobrite experiment which I tracked down to uneven application of the paste & uneven exposure to UV. Is it possible your mix was not thoroughly mixed?

[cihensley@aol.com]

HarrySmith:

Thanks. MEK is a solvent like acetone, no mixing.

Chuck

[old_phone_man]

You are right.  The one side looks fantastic.  Since you did this in 2 stages (I assume by dipping one end then turning it around and dipping the other end), did the crazing happen during the first dip or the second?  I just wonder because the crazing appears to fall right around your line of demarcation.  If the crazing happened on the second stage of dipping could it be the first dip left some contamination?

Just a thought.

[cihensley@aol.com]

old_phone_man:

Thanks for the thought. The end of the part that looks good is also crazed. And, the receiver cap (which turned out good) was done last.

Chuck

[old_phone_man]

Ah Yes, when I looked at the enlarged photo I can now see the slight crazing on the side of the handset.

[Bill]

Chuck -

Just trying to keep up with your results here. Good stuff!

I think of "crazing" as a network of fine hairline cracks, and I don't see any in your photos. By any chance are you referring to the mottled / blotchy / cloudy areas that show up in some of them? If so, it is interesting, in that the blotchy stuff was originally present on my red 500 handset, described and photo'ed in post #5 in the other thread. Wiping with MEK removed it, though it took several wipes and a lot of surface plastic removal. And apparently for you it caused the blotchiness? I have no idea what conclusion to draw. Might it be useful to try a brush or rag, loaded with MEK, on the blotchy areas to see if they can be removed? Then follow with an MEK dip to clean up the surface.

I'm tryin' t' think, but nuthin's happenin!"
                                            - Curley

Bill

[cihensley@aol.com]

Bill:

You are correct. When I think of crazing I too normally think of fine hairline cracks. I was searching for a term to describe the result. Maybe I should have described it as "undesirable blotching."

Chuck

[cihensley@aol.com]

I re-sanded the handset, washed it in water and soap and handled it with latex gloves. I also heated it with a heat gun prior to MEK dipping. The result was much improved but there still was some undesired blotching on part of the surface. What I can't understand is why there is no blotching on the interior surfaces, that receive the same amount of MEK. Next I will try the dipping with acetone instead of MEK and/or mixing some other solvent, probably lacquer thinner, with the MEK. I am pursuing this because the surface the that is not blotchy is close to new plastic in appearance.

Chuck

[old_stuff_hound]

I re-sanded the handset, washed it in water and soap and handled it with latex gloves. I also heated it with a heat gun prior to MEK dipping. The result was much improved but there still was some undesired blotching on part of the surface. What I can't understand is why there is no blotching on the interior surfaces, that receive the same amount of MEK. Next I will try the dipping with acetone instead of MEK and/or mixing some other solvent, probably lacquer thinner, with the MEK. I am pursuing this because the surface the that is not blotchy is close to new plastic in appearance.

Chuck

Kind of reminds me of mottling on candles caused by too much oil in the wax.

(Let me preface this by saying I have no idea what I'm talking about! :-) My guess is that you've still got surface contaminants, perhaps embedded in the plastic. It looks almost as though a discolored surface layer is "pulling back" and revealing pure-colored plastic underneath. I know the retrobrite process converts oxidized plastic constituents into a different form that are not discolored. Perhaps you've still got a layer of oxidized, discolored plastic that reacts with the MEK and gives you this effect? That would explain why you're not getting it inside -- that plastic has not been exposed to UV.

So then the options become:1. Sand more, then MEK, or 2. Retrobrite what you've got & see if the mottling disappears. I'd be really interested in the results of #2! :-)

Another random though -- did you sand the inside? Probably not, right? Could the sanding be causing it somehow?

[Bill]

Old_stuff_hound -

Your thoughts tweaked something in the back of my mind, so I went rummaging. Way down at the end of one of Briny's earlier threads
    http://www.classicrotaryphones.com/forum/index.php?topic=1989.0
Dennis talked about mold growth on plastic. The blotches in Chuck's photos above, and in my photo earlier, look just like the way mold grows. The irregular growth pattern (blotches) plus the fact that it has sunk down into the plastic, suggests that Dennis may have hit the answer. And if so, removal of everything down to the deepest penetration of the mold is probably the only way to get the blotches out. At least that was my experience.

There is some ingredient in plastic that feeds mold (which will eat most anything, of course). Most of us have seen mold on a poorly-stored plastic phone. As Dennis observed, you can sand off the surface mold, but it will come back if you don't dig it all out, or kill it with bleach. Even after you kill it, though, the discoloration will probably remain, so bleach alone will not be the answer..

Thoughts? Chuck? Dennis?

By the way, don't lose track of the fact that in this thread, at least, Chuck isn't using retrobright, so thoughts regarding UV don't mean anything.

Bill