CLEANING NEGATIVES The films of negatives are best cleaned when wet. Usually they are merely wiped over with a piece of wet cotton-wool ; but to remove a dirty or messy appearance from a dry negative use cotton-wool soaked in methylated spirit, rubbing very lightly to avoid reducing the den sity. The metal-polish reducer (see " Baskett's Reducer ") may also be used for cleaning the dried film, but must be used very gently.
It is generally the glass side, not the film side, of a negative that requires cleaning. In the process of manufacture some stray emulsion may get on the glass side, which, if allowed to remain, would show in the print. Emulsion streaks are best removed when wet by rubbing with damp table salt ; but the same method answers when the negatives are dry.
To clean off the films from " waster " nega tives that have been varnished, soak them in a hot solution of soda or potash, and then rub with a stiff scrubbing-brush, finally rinsing ; if potash is used, do not let it touch the fingers.
Soaking in water containing a little nitric acid answers for unvarnished negatives, scrubbing or scraping afterwards if necessary. The follow ing solution is also recommended for removing unvarnished films : Citric acid i oz., hydro chloric acid 2f oz., water zo oz. Soak iu this for-an hour or two, scrub, and finally rinse.
An excellent cleaning and polishing mixture for glass consists of the following : Rain or soft water . . . i oz.
Powdered pumice-stone . . i „ Whiting or prepared chalk . if „ Liquor ammonia . . . f „ Apply with a piece of chamois leather or flannel, and polish with a clean rag or soft paper.