ABSTRACT
Chlorhydroquine has a number of characteristics which make it desirable as a negative developer. Used alone it is said to be five times more active than hydroquinone; used with other agents, it is reported to be somewhat less superadditive than hydroquinone with metol and Phenidone—a potentially valuable characteristic. An advantage of using distilled water and mixing researchers own solutions are that sequestrants are usually not necessary. They may be necessary with ascorbate developers even when distilled water is used, to sequester contaminants introduced by other ingredients. By a careful choice of developer it is possible not only to vary the threshold sensitivity of an emulsion but to alter its characteristics. Ascorbic acid itself is not specified in most formulas. The usual form is sodium isoascorbate. Ryuji Suzuki states that using the acid form or the salt makes no difference if the final pH is the same.
