Keuffel & Esser 1744

This slide rule (click to enlarge the photo at right) was made around 1897 and sold by Keuffel & Esser. It may have been actually manufactured by Dennert & Pape (in Germany); they made the earlier versions of this model and I'm not sure when Keuffel & Esser actually took over the manufacturing themselves. I've posted this up on my collection web site, including high resolution scans and lots of details.

This one posed an interesting restoration challenge that I had not run into previously – sometime in its history, someone spilled a liquid onto one side of it, and then let the liquid evaporate without cleaning it up. This left a layer of gunk on the slide rule that looked a lot like rust, and was quite difficult to remove – no solvent I have would dent it; I had to soak and abrade it (using Bon Ami). Some staining still remains; I could see under a microscope that the colorant has migrated into the plastic.

In addition, this slide rule had 110 years worth of the grey “gunk” that seems to accumulate on anything that humans touch. I probably really don't want to know what's in it! Usually this gunk cleans off easily with soap or alcohol, but on this slide rule some of the gunk had hardened into something resembling granite. To clean the slide's tongues and grooves I had to resort to carefully picking off the rocky gunk with a dental pick – hard work for these old eyes...