Film Fixers

The fixer came a lot later than the developer. The first attempts to use the blackening of silver salts by light in any sort of artistic manner date back to the early eighteenth century but the developer did not begin to make an appearance until Daguerre used mercury vapour to make a latent image visible. In the meantime, various pictures had been produced but attempts to make the image permanent had not met with much success. The main function of the fixing solution is to facilitate the removal from the emulsion of silver halides that have not been affected by light. If they are not removed they will eventually blacken and obscure the image. The manner in which the fixer accomplishes this task is not a simple one. It converts the halides into soluble silver compounds but the conversion is a two-stage process. The first stage produces a compound that is barely soluble and is also unstable. Only after that stage is passed are the complex soluble compounds formed that can eventually be removed by washing. The capacity of a fixing solution is very difficult to determine. It is evident that the more work it has to do, the sooner the fixer is exhausted. That may account for the recommendation by one authority in the 1950s that for an eight-exposure spool, at least 60 oz of fixer should be used and then discarded. The pH should be around 4.2 to 4.6. If it is higher than 4.6 an appropriate quantity of acetic acid could be added but when working with small quantities it is more practicable to discard it.