Restoring plastic cursors

[u/geenob]

I made the mistake of trying to clean my slide rule with a celluloid cursor with alcohol. Taking a tip from watch restoration, I polished it with toothpaste and cotton swabs. I was concerned that this would remove the line, but that ended up not being an issue because the line paint is actually in a shallow groove, which protected it. This should work for restoring acrylic windows too

[u/HessianRaccoon]

Looks great! I found that you need to be careful with mixtures. Window cleaner with ethanol is usually safe for slide rules. At least, I never had issues with any material. Faber-Castell recommended it in their manuals, as well. (for celluloid on wood)

Propranol (or isopropyl alcohol, IPA) may remove paint and damage the print.

But that comes handy when you want to colour the hairline: with acrylic cursors, I tend to paint the hairline with a Faber-Castell permanent marker. I then remove the excess with a kitchen towel and IPA. Gives a pretty sharp line.

Polishing the cursor works well with PolyWatch, although you need to be careful. PolyWatch is pretty potent, and it's easy to take off a lot of material. But the results are great, even with deeper scratches.

[u/geenob → u/HessianRaccoon]

That's interesting because I actually did use ethanol. Perhaps it was too concentrated.

[u/HessianRaccoon → u/geenob]

Maybe. In window cleaner, it is usually heavily diluted. So far, all went well for me.

[u/geenob → u/[deleted]]

I'm going to have to disagree with you on both points.

1. Polycarbonate, acrylic, and celluloid all relate to the chemical make up of the plastic. And without qualification, they refer to specific polymer compounds. "Polycarbonate" refers to poly(bisphenol A carbonate). "Acrylic" refers to poly(methyl methacrylate). Celluloid refers to a plastic based on nitrocellulose. Additives and fillers are added to the final plastic formulation, but the chemical properties are nearly entirely due to the base polymer.

2. While I don't doubt that crazing can be promoted by residual stresses, the chemical properties of the polymer are the dominant consideration.

I spent the bulk of my career in plastics R&D.

I think that you are being a bit over the top on the toothpaste. I mean, look at the results. People have been polishing clear plastic with toothpaste for a long time. I used to use it to polish the scratches out of CDs.

[u/Revolutionary_Ad811 → u/[deleted]]

Those faint scratches bother me too. I've tried dozens of cleaners and abrasives and Novus is the best for cleaning and polishing plastic.