PYRO FOR BROMIDE PAPER Pyro when properly used gives exquisite brown tones on bromide papers, the pyro-acetone formula being perhaps the best : A. Pyro . . . 220 grs. 5o g.
Sodium sulphite . 1,320 „ 300 „ Sulphuric acid . 3o mins. 6'25 ccs.
Water to . 10 oz. 1,000 „ B. Acetone . . oz. 55 g.
Water to . . xo „ 1,000 ces.
Use equal parts of A and B. The tone can be altered by varying the quantity of acetone.
The following formula also gives good colours, but the mixed developer should be used for one print only. Solutions A and B, mixed in equal parts, may be used for lantern slides. Pour solutions are required, from which two work ing solutions are made up, one for the actual development and one for clearing :— A. Pyro . . . 55 grs. 13 g. Potassium meta bisulphite . • 40 ,, 9 ,, Sodium sulphite . I oz. 11O „ Water to . . 10 „ 1,0o0 ccs.
B. Sodium carbonate. 64o grs. 146 g.
Water . . . 10 OZ. I,000 ces.
A developer ready for use consists of equal parts of A and B.
C. Potassium perman ganate . . 240 grs. 55 fl• Water . . . xo oz. 1,000 ccs.
D. Common salt I oz. IIo g.
Water . . . 10 „ i,000 ccs.
Sulphuric acid . 4 dribs. ,, The clearing solution is made by adding I oz. of D and 15 mins. of C to 10 oz. of .water. The
developer (A and B) is poured over the bromide paper, which, when fully developed, is rinsed in water and then flooded for not longer than 3o seconds with the clearing solution. It is next washed for about a minute and fixed in an acid fixing bath, preferably potassium meta bisulphite and " hypo." Dr. Just's pyro developer is as follows : A. Pyro . . . 20 grs. 4'5 fl• Glacial acetic acid 18 mins. 4 ccs. Potassium meta bisulphite . 9 grs. 2 g.
Sodium sulphite . 15o„ 34 ,, Water . . . 10 oz. 1,000 ces.
B. Potass. carbonate . 85 grs. 20 g.
Water - . . Io oz. 1,000 ces.
Use equal parts of each. The developer is almost colourless at first, but rapidly turns brown. For many papers the addition of 6 drops of a I in 5o solution of potassium bromide to each 4 oz. of mixed developer is necessary. After develop ment the print should be rinsed in a clearing bath of very weak acetic acid in order to re move stains, and is then washed and fixed in an acid bath. The addition of a few grains of hydroquinone to the pyro solution has been advocated.