microscopic slide cleaning and maintenance
An old technique to clean used slides is to just toss them in a jar containing equal volumes of distilled water, ethyl alcohol 95% and xylene. Shake from time to time. When needed wipe them dry using a clean, lint free cloth and use. 

The techique was at the time (1930's?) in use in the lab of prof. Baudet (Veterinary parasitologist, Utrecht University) and is mentioned in several editions of the "Précis de Microscopie" by Maurice Langeron. 

Langeron mentioned that the slides treated that way were "perfectly grease-free". 

Another method is to wash the slides, rinse in distilled water and store for some time in a mixture of ethyl alcohol and acetic acid. 

When on a tight budget, used Carnoy fixative was (is?) used. 

This is a trick that was (is?) in use at some botanical labs in Eastern Europe. 

It's mentioned in some of the German literature on microtechnique, if memory serves me right in Braune, Leman and Taubert's "Pflanzenanatomisches Praktikum".