The fur between the keys is removed and the overall machine polished-up nicely.
The keytops themselves were first cleaned of the runny 'goo' by simply wiping it off with tissue-paper. Much of the remaining dirt and expanded 'ink' was removed with a rag plus soap and water. The top surface and the sides of the octagonal keys was finally 'polished' with metal-polish - this makes the surface a little brighter again without damaging too much. Especially the white, dimpled (odd-numbered) keys have deteriorated - the old plastic has shrunk, cracked and curled up. The keytops are still not completely cleaned, but the keyboard is now serviceable and no longer 'icky' to touch.
To clean between the keys without removing them (a non-trivial procedure), a 1/4" square wooden slat wrapped in a damp rag was used to get between the stems. This slat with cotton rag with some metal-polish was next used to clean the stems themselves. Great care was taken to not rub the top-plate with the metal-polish, as this would have damaged the finish!
The case of the Comptometer is made of copper-plated steel that was then given a clear lacquer top-coat. On the front-right corner these layers are worn-through from regular use. (Quite some information about these Comptometers is on the internet at various sites, for example a lot of information on the different types and on the mechanism is on John Wolff's Web Museum site.)
The copper-coloured case was washed overall with a damp cloth with soapy water. With a wooden toothpick the dirt around the edges of the raised decorations was cleaned off.
Most of the dark stains are corrosion and/or dirt of the copper underneath the lacquer. For example; most of the dark spots on the top-plate between the stems clearly show the hole in the lacquer, with surrounding discolouring.
On this machine the list is scratched and a bit difficult to read. Even though this machine was manufactured around 1935, the list still starts with Dorr E. Felt's first US patent 366,945 for the Comptometer issued in 1887.