The best piece of advice I can give concerning cleaning or restoring a valued slide rule is simply this: don't.
That's not to say it can't be done successfully ... but with any restoration job you run the risk of damaging the object you are trying to preserve. If you are interested in the rule largely as a conversation or display piece, you are probably better off leaving it the way you found it. But if you are interested in using the rule functionally, or in simply restoring it to its former glory (and who among us doesn't have that urge?), then there are a number of methods you can try depending on the source material you are working with. After all, every rule was intended to be manipulated by hand, and therefore required regular cleaning and care to maintain usability. However, given the lapse in regular use most slide rules have received, cleaning today can take on more of a restoration role, hence my warning up above.
Given the interest on this subject, I thought I'd present my general experience with different cleaning methods and my preferred choices for slide rule upkeep on this page. My goal is simply to provide information, not advocacy, and the standard warning of caveat emptor applies if you attempt any of these yourself. As I've recently expanded the material on this topic, I thought I would break it up into multiple pages to make it easier for people to find the info they are looking for. You will now find a table at the bottom of this page directing you to my revised pages on wooden (including celluloid-covered), plastic, and metal rules, along with pages on slide rule cursors and cases.
Before you begin, carefully inspect your slide rule for any signs of damage that may be exacerbated by attempted cleaning. Pay close attention to the state of the cursor assembly, as well as all visible surfaces of the rule. In particular, watch for rotting plastic end pieces, loose strips of celluloid on wooden rules, and pealing painted surfaces on aluminum ones. Simple surface dirt and grime can be cleaned quite easily, and even considerable yellowing can often be significantly reversed. You can even "re-ink" faded scales and cursor hairlines in many cases if you are careful and patient, although this depends greatly on the source material you are starting with. However, damaged or overly brittle surfaces are best left alone if they don't detract from the general use or look of the rule.
In some cases, it is better to partially disassemble a slide rule in order to thoroughly clean it. This is often not necessary, and not all slide rules are meant to come apart anyway. In fact, most cursor assemblies can be cleaned quite easily without disassembly. Whatever you decide, make sure you feel confident that you can put everything back together again before you begin (especially an issue when accurately lining up hairlines on duplex rules)! One special concern is the cursor assemblies of older K&E rules, as they can be very brittle due to age and may crumble if you try to adjust them. This condition is known as KERCS (K&E Rotting Cursor Syndrome), and is discussed on my Cleaning Cursors page. The only tool you are likely to need for disassembly is a good set of jeweler's screwdrivers, which can be easily obtained at any hardware or electronics supply store.
Best of luck with your rule!
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