Silver nitrate . . 2 „ zoo g.
Potass. iodide . . 2 grs. IP Shake well, stand in sunlight for a day, and filter into a glass dipping bath, when it is ready for use. The following albumen solution must also be prepared and kept ready at hand for use after collodionising : Albumen (fresh white of egg) . . . 8 oz. Boo ccs.
Liquor arnmoni‘T . 2 drms. PI Potass. bromide . io grs. .4 g.
Potass. iodide . . 5o „ 2'0 „ Distilled water . . 3 oz. 30o ccs.
The albumen must be well beaten up with a silver fork, the bromide and iodide mixed with it, the water and the liquor ammoniae being then added. The mixture should stand twenty-four hours before use, and then be filtered through muslin. Take one of the plates prepared with the substratum, coat with the iodised collo dion, drain, and move to and fro in the air so that the ether may evaporate, place at once upon the dipper and immerse in the silver nitrate bath. A deep ruby light is not neces sary, an orange or a deep yellow light being quite safe enough. The plate must be moved up and down in the silver bath a few times, allowed to stand for two minutes, taken out, the silver drained off, and then washed for a few minutes and drained, but not dried. While the surface is still damp the plate is covered with the albumen solution, drained, and again coated with the albumen. When dry, the plate must be treated in order to make the bromo-iodised albumen more sensitive to light, for which pur pose the following bath is used : Silver nitrate (recrys tallised) . . . 60o grs. 6o g.
Distilled water to . 20 OZ. 1,000 ccs.
Glacial acetic acid . no drms. 1 cc.
The plates are allowed to remain in this bath for two or three minutes, washed well, and flowed over with a nearly saturated solution of gallic acid, and finally dried in a. warm dark place. The plates are then ready for exposing. The time of exposure will be about fifteen times as long as an ordinary modern gelatine lantern plate. Over- is better than under-exposure. The following pyro developer should be used : A. Pyrogallic acid . 96 grs. too g.
Alcohol to . . I oz. 50o ccs.
B. Potass. bromide . 12 grs. 125 g.
Water to . . 1 oz. 50o ccs.
C. Ammonium carbon ate . . . 8o grs. 84 g.
Water to . . t oz. 50o ccs.
To prepare the developer for use, 12 drops of A are mixed with .1 dram of B and 6 drams of C. The image soon appears, but will be thin and usually requires to be strengthened by redevelop ment, which is done by applying a small quantity of the following developer, after washing off the first developer : Pyrogallic acid . . 6 grs. 4 g.
Distilled water to . 3 oz. 85 ccs.
Citric acid . . . I4 grs. i g.
Before using this, add a few drops of a solution of 3o grs. of silver nitrate in t oz. of water. As i soon as dense enough, the plate is fixed in a solution of sodium hyposulphite (4 oz. to zo oz. of water), washed for about five minutes, and dried.
Many other formulae have been advocated, some much more simple than the above and without the use of collodion, but the process described probably gives the most satisfactory results and offers fewer opportunities for failure.