Rusty brown stains on photographic negatives are caused by damp, and are known as silver stains. If the stains are old. it is, as a rule, impossible to remove them, hut either of the following methods of treatment will make them fainter. Soak the negative and immerse for a short time in sulphocyanide of ammonium 1 dr., water loz., and transfer to nitric acid ldr., water 1oz., without any washing. Or try the following. Thiocarbamid 6 gr., citric acid 10gr., chrome alum 20gr., water 2oz. Allow the negative to soak in this solution, and the stains will probably be reduced. In either case, the removal of the stains will be greatly assisted by a little gentle friction with a tuft of wool.