A brief description is given of the function of the Central Research Laboratory, Amsterdam. Originally set up to research into new methods of conservation/restoration and treat difficult problems from state museums and collections, it is now open to private owners and collectors. All leather (except gilded leather) is fumigated with ethylene oxide when it enters the laboratory. Full documentation follows, then joint discussions on possible treatment methods. Recent research has investigated dye colour changes in which two photochemical reactions may occur: the first one on the leather altering its pH; the second, the increased acidity altering the dye's colour. A non-aqueous alternative to potassium lactate was found in imidazole (2% isopropanol). In the discussion, it came out that after treatment RH should not rise above 60%, as hydrolysis of imidazole could darken the leather irreversibly. Red rot in leather needs prior deacidification with ammonia vapour.