Early Work In Photography
A Text-book For Beginners

Weights and Measures, Other Useful Formula. 97 For normal exposure take equal parts of each solution. For over exposures add a few drops per ounce ot ten per cent potassium bromide solution. Bear in mind the following points regarding this developer. . Pyro is the developer and does the work, sulphuric acid being simply a preservative; sodium carbonate is the accelerator that forces pyro to do the work; potassium bromide is a restrainer that prevents the work being done too quickly ; sodium sulphite keeps the work clean.. Sodium carbonate opens the pores of the gelatine and en- ables the pyro to work vigorously, but too much carbonate causes fog and clogs up the half-tones of the negative with detail Too much pyro gives too much contrast; too little pyro gives a weak negative lacking contrast. Sodium sulphite prevents discolouration and gives bluish-black negatives, too little causes yellow negatives., Therefore: for normal development of correct exposures use equal parts of pyro, carbonate and sulphite; but it yellowish negatives are required reduce the amount ot sulphite. . , , . In over-exposure use pyro 2 parts, sulphite 2 parts, carbonate 1 part, bromide (10 per cent, solution) from 10 to 30 drops per ounce. , 1 In under-exposure use pyro 1 part, carbonate 2 parts, sul- phite i part, water 1 part, and allow plenty of time tor development. . , 1 Should pyro-developed negatives be much discoloured after fixing and washing, they can be cleared by a few minutes’ immersion in the following Clearing Bath. A ■ .. I ounce Alum .. •‘ 1 X Sulphate of iron .. 3 ounces (= Water .. ■ • 20 ounces When dissolved, add slowly Sulphuric acid .. 120 minims They must then be again well washed. 480 grains) 1440 » Metol Developer. A.-Metol Dissolved in water Add sodium sulphite .. B.—Potassium carbonate Water 154 grains 35 ounces 1543 grains 12 ounces