STAINS, REMOVING Stains on Hands.—Pyro and some other de velopers stain the fingers by prolonged use ; care must be taken to avoid putting the fingers in solu tions, excepting when absolutely necessary. Any tendency to staining may be entirely obviated by rinsing the fingers and immersing them for a few seconds in an acid fixing-bath immediately after putting them in the developer. Rinsing and drying must follow at once. An acid fixing-bath or a solution of potassium meta-bisulphite will also remove stains of permanganate and many other photographic substances. It is a good plan to bathe the hands in hot water and then, before drying, rub glycerine into them.
Stains in Intensification.—Stains should not arise if the negative is in good condition and if all the previous work.has been carried out correctly. Yellow stains that may appear during mercurial intensification are due solely to imperfect fix ing of the negative. Insufficient washing after fixing will also cause staining. There is no method of removing these stains. In intensi fying by silver, Wellington's method, surface staining may occur if the operation is very pro longed, the cause being the same as in a long or forced development. These stains may be easily removed by methylated spirit applied as directed under the heading " Reducing Negatives by Mechanical Means," or they may be treated by thiocarbamide or the "hypo " and ferricyanide solution.
Stains on Negatives.—When negatives show staining after development and fixing, the char acter of the stain will always indicate the cause and the cure. Iridescent markings round the edges of a negative are almost always caused by using old plates, especially if the plates have been kept under bad conditions or forced in development. They may be removed by means of thiocarbamide or by methylated spirit applied with friction. Surface stains, semi-iridescent,
with rainbow-coloured markings, are sometimes seen on negatives otherwise perfect. These are due to scum on the developer, caused either by using the same solution for several plates in succession, or by mixing the developer in a measure without rinsing after previous use. A weak thiocarbamide solution will remove these stains almost instantly. A weak " hypo " and ferricyanide reducer will also remove them in a few seconds.
Stains on prints show yellowish brown stains, semi - iridescent, if the surfaces cling to the dish or to another print during the first few seconds of washing in plain water before toning. These stains are most frequently attri buted to " hypo," but they are in reality silver stains. There is no method of removing them satisfactorily. Similar stains may develop during fixing, or in the first washing water after fixing, if the prints are allowed to ding together ; and they cannot be removed satisfactorily. Platino type prints may develop yellow stains after wash ing and drying if the clearing has been imper fectly or carelessly performed. It is difficult to remove these stains without injuring the print ; the best treatment is a strong solution of hydro chloric acid, s part of pure acid to so or 12 of water. Two or three successive baths of acid may be used, the prints being afterwards washed well. Prints on bromide or gaslight papers may be stained from the same causes as given under the sub-heading above, " Stains on Negatives." The treatment is the same, excepting that solu tions about one-fourth of the strength are used.