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I would like to remove the surface rust on a steel paper-support. However, I would like to leave the painted markings on it intact. Does anyone have an idea how to remove the rust without affecting the black paint? Re-painting it myself afterwards is really not an option for me.
I must add that the markings are just painted on, not engraved/stamped and infilled, and the paint looks quite thinly applied and fragile. A few of the numbers are already a little faded.
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This sounds like you are asking about museum-level restoration techniques. Research that topic. I expect you will find that it involves pin-size picks and scrapers and quite possibly some esoteric chemicals and finally a finishing wax. Certainly not a dunk in vinegar, Coca-Cola, or even Evap-O-Rust with a wire brush, so you are right to not just jump into this project. Not my field though, so I won't guess more.
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Okay, I may be able to help since I've just had this issue with a large restoration project.
What you need:
- methylated spirit (not lacquer thinner, not surgical spirit, please)
- cotton buds (do not use these longer than they can handle, otherwise the spirit will get everywhere and the cotton will peel of and jam your machine)
- toothpicks (sometimes I use metal toothpicks, but you want to build up to that and be very sure that your toothpick has a sharp top so you don't hit your painted markings)
- lots and lots of towels
What you need to do:
1. Be very careful. I'm sure you know this, but meths are not to be underestimated!
2. Place towels all over the places you are not even getting close to (keyboard, namely) and remove the ribbon (methylated spirits obliterate ink).
3. Keep your methylated spirit in a closed container when not being touched. I keep it in a spray bottle and spray my cotton buds over a towel.
4. Soak your cotton buds. Place this on the rusted part and hold for a few seconds. Play around with this (safely!) so that you find out the shortest amount of time needed.
5. Take your toothpick and scrape/poke the rust. You will see it dissolve into a clay-like consistency.
6. Take a towel and dab/wipe it off, depending on how close the paint is.
This will take a long time - it took me about two hours cleaning a rusted bar. On the other hand, there is absolutely no rust left and when I put paper through the typewriter there is no transfer.
Good luck!
I should mention that I have never placed methylated spirits on paint, decals and keyboards before so I cannot give you an indication of what would happen. I find my methylated spirit in my local paint shop and it is very cheap and evaporates quickly. On the other hand, it has a strong smell and some brands put arsenic and purple dye in the solution to stop people from drinking it (yikes!).
Hope everything goes well.
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I would start with car wax. Almost all retail car waxes have a bit of abrasive in them to remove the oxidized paint and that might be all you need to remove the rust, depending on your situation. Just be careful at first and work on a small area. If that doesn't work then you might need to try more drastic measures.