Readers of this 'blog might recall that I collect working slide-rule tie-clips, and readers of my defunct LJ might recall that I have a collection of ordinary slide rules (to which I almost never make additions, because I had limited ambitions and most of these have been met).
Recently, the Woman of Interest mentioned the slide-rule tie-clip collection to her maternal grandmother, who volunteered that her late husband (grandfather to the Woman of Interest) had had one, and offered to give it to me. I was happy to accept, as none of my other such tie-clips has a family significance for me. I also learned that this man had had a slide rule, a Pickett & Eckel of unknown composition, but that it was not in working order; the rules wouldn't slide, and there was a lot of white powder on the device. I offered to fix it and return it, but the outcome of that offer was that it was given to the Woman of Interest, for whom I was to fix it.
The slide rule arrived on Monday (along with a bag of premium salt-water taffy, perhaps to sustain me as I worked on the device). It proved to be a Model 500, and I decided that it were of a light-weight metal with plastic laminate for the scales, and that the white-stuff were probably corrosion product. Some of Pickett's later slide rules were definitely made of aluminum, and aluminum oxide powder is typically white, but I didn't find confirmation on-line that this model were made of aluminum. Nor was I sure that other metal parts wouldn't be damaged by water; the braces, bolts, and rivets might be of a different metal, and the indicator spring was surely not aluminum. Meanwhile, I had to be careful about that plastic laminate as well.
Having gone to the local drug-store for something else, I wandered around the aisles looking for something to use to clean the slide rule, and saw jars of petroleum jelly. That seemed a great choice; it could be used to
wet areas without water, loosening and suspending the oxide and other dirt. Any residue could function as a lubricant and water repellent, and it shouldn't reäct significantly with the metal, plastic or marking colorant. There would be no odor. The only down-side is that the residue will tend to hold onto particulates with which it has come into contact, but occasional wiping should fix that. (Unfortunately for the store, I already had a tub of petroleum jelly at home, but I'd bought that from them, years ago.)
Anyway, I carefully disassembled the slide rule, cleaned it with the petroleum jelly (and the indicator plates with hot water), reässembled it, and made sure that the scales and indicator plates were in good alignment. The slide rule is back in working order.