Sooo, I was thinking … yes, I do that on occasion … about rust.
Many old camera’s that I get have been stored away for many decades and have developed rust/oxidation. Scrapping this stuff off with sandpaper is not the nicest way of removing it as it scars the surface around it.
Most old camera equipment is chrome plated brass (or in some cases it is nickel or nickel-chrome). This makes it look shiny nice and also creates an oxidation barrier over the brass material that most of these old cameras and lenses are made of.
The chrome plating eventually does oxidize/rust if given enough time in poor storage conditions.
Recently I got a hold of a Canon rangefinder with lens that had numerous spots on both pieces, so I thought I would look into removal without abrasives. I ran across some articles from BMX bicycle forums about how they remove the stuff … oxalic acid. They would take a large plastic tub and mix the stuff up and just let the bike parts soak in it for a day … and the rust would just dissolve.
The easiest way of getting a hold of oxalic acid is by getting wood bleach. Comes in various size tubs of crystals … I got the smallest tub I could find, as you do not need much of it.
Soooooo, I gave it a shot.
This is the image of the lens (from the seller, as I forgot to take a picture of it myself before I attempted the acid bath).
The rusty areas are a crusty orange.
I took the lens apart to remove all the lens element components. This left the upper assembly which included the aperture section.
I took a glass spaghetti sauce jar and filled it with cold water, then I added one rounded teaspoon of wood bleach crystals.
Be warned that you do not want to inhale this stuff, nor get any crystals or liquid on you.
I let the section soak for 3 hours, then scrubbed the rusty areas with a scouring pad. I let it sit for another 3 hours. Scrubbed again and then used some paper towels to dry it off.
I then drowned it in lighter fluid (it is recommended to wash the item in water, which is what I would do in the future before the Ronsonol) and worked on cleaning the aperture area, as I did not want the solution to crystalize in that area … would have been better to have disassembled it further so not to have that part in the solution.
This is the after shot of the lens mostly reassembled. It may not look all that different … but the brown areas you see are where the orange crusty rust was … it now reveals the brass underneath (the chrome plating rusted away).
Note that the painted numbers/lines were not removed during the acid bath process.
There are other solutions that are written about (including using Cola) and I gave this one a chance.