Cleaning Plastic Slide Rules

If you are looking for tips on cleaning celloid-covered wooden rules, please check out my Wooden Rules page.

It is something of a misnomer to lump all plastic slide rules into the same category, given the wide range of actual materials used under the generic term "plastic." Many people tend to have a negative view towards slide rules of this sort, presumably reflecting their view of plastics as low-quality items. This is hardly a fair assessment, and some of the highest quality slide rules ever made were made of plastic (any top of the line Faber, Aristo, or Nestler should quickly dispel any concerns). Even K&E switched to all-plastic for their high end models by the 1960s. I think the problem stems from all the cheap consumer items made of poor quality plastics that we often encounter in life (including some slide rules, like the awful Sterling/Precision models). But well made plastic rules actually have a lot of advantages over wooden ones - they generally don't stick, warp, or break as easily, and seem to withstand age effects better (with some exceptions which I'll get to in a moment).

Cleaning a Plastic Rule

Cleaning these various types of rules isn't all that different, regardless of who made them. As always, a mild gentle soap (like diluted Palmolive) works best. For problem rules, I'd recommend soaking them for some time in warm diluted Palmolive (preferably disassembled, if you can) and then wiping with a clean wet cloth. Not all plastic rules aren't meant to come apart, however, so try not to force things too much.

In problem cases, it's possible a wet Scotch pad may be useful in gently dislodging dirt after soaking, but only if your rule has engraved scales (as a warning, examine what happened to my printed Pickett metal slide rule). Check out Walter Shawlee's Slide Rule Universe for an example of how he rescued a poor misused K&E 4181 with this method. As always, however, I would not recommend using a Scotch pad or any other abrasive method on a printed plastic rule, as it might very well destroy the ink (or even the surface of the rule, depending on composition). I also don't recommend the use of erasers either. Apparently regular pink pencil erasers can be safe for spot cleaning on some rules (like my Nestlers), but white plastic erasers are frowned upon (I've never tried either type on a plastic rule, so you are on your own here).

Ageing Problems

Despite their general resistance to age-induced warping and such, plastic rules do have their own unique set of potential problems. One is fading of the colour accent stripes used on many high end German-made rules (a particular concern when it comes to cleaning). If this has happened to your cherished rule, not to worry ... Larry Stewart has developed a technique for restoring faded accent stripes using watercolour pencils. Check with him for more details.

A more unusual problem is an offensive smell that some old slide rules (and their cases) can produce. This is generally believed to be due to "out-gassing" of the various plasticizers added to the plastic (typically PVC) during production, in order to soften the rule and give it the right feel. As you may imagine, plastic design was something of an art as well as a science, and certain manufacturers developed better choices than others. The out-gassing of these volatile substances is not generally a problem, unless the rule has been sealed away in a tight case. The smell can build up over time, and be hard to deal with once it does. One thing that I find works well is those smoke/pet odour removers available at any hardware or grocery store (shown on the right). I always keep one open at the back of my slide rule rack, and it also helps with the musty odours emanating from some of my older slide rule books. I would recommend that you periodically open the cases on plastic rules from time to time, or let them sit with the cases cracked open for air to prevent this problem.

Adjusting a Plastic Rule

Personally, I've never had a problem with the slide sticking in a plastic rule. As such, I'm not really in a position to advise much on the subject of lubrication. I know some people like to use silicone grease in their higher-end German slide rules, but I've never tried this. Probably a simpler option for those with problems in this area is one of the newer "dry" Teflon-based lubricants. As mentioned on Metal Slide Rule page, the term dry is a bit misleading as these are actually in liquid form when you apply them, and subsequently dry to leave a Teflon coating behind. There are numerous brands available, and one of the most common places to find them are in the bicycle section of your local general goods store. I've heard of several success stories using this method on high quality German rules, but I've never attempted it so you are on your own here. And I have at least one report where a Teflon-based lubricant blistered the plastic on a Pickett cursor assembly, so I'd be rather hesitant to try this method on a cherished rule.

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Page last updated on November 27, 2002 -
All material © 1999, 2002 by Eric Marcotte, Ph.D.