COLLODION EMULSION A suspension of various silver salts in collo dion, and used for printing-out papers, trans parencies by development, and negative work. The simplest of all collodion emulsions to make is that for printing-out paper, or, as it is some times called, collodio-chloride paper. There are numerous but those given in the next column and in the first column of p. 119 have been found of great practical use.
Valenta's Formula Lithium chloride . . . o.9 g.
Strontium chloride . . 1.8 „Absolute alcohol . . . to ccs.
Glycerine . . . so Dissolve by the aid of a gentle heat, and add Celloidin collodion (3 %) . 95o ccs. Then add— Citric acid . . • • 5 g.
Warm alcohol . . . q.s.
Enough alcohol should be used just to dissolve the acid. Shake thoroughly, and add :— Silver nitrate • . . 16 g.
Hot water . . . . 20 ccs.
This should be added in small quantities at a time, shaking thoroughly between each addition. Allow the emulsion to stand for twenty-four hours, then filter and use.
Hanneke's Formula A. Celloidin collodion (4 %) . 62o ccs.
Ether . . . . too „ Absolute alcohol . . 30 „To this add B. Silver nitrate . . • 25 g.
Distilled water . . . 25 ccs.
Absolute alcohol . . I 20 „ Then add in small quantities, shaking well after each addition and observing the order given : C. Calcium chloride (crystal) . 4 g.
Distilled water . . . 4 ccs.
Absolute alcohol • • ,,D. Citric acid . . . . 5 g.
Distilled water . . . 5 ccs.
Absolute alcohol • . 30 „ E. Castor oil . . . . 7.5 ,, Glycerine . . . . 7.5 „ Absolute alcohol • • ,,For solutions B, C, and D, the salts or acid should be dissolved in the water by the aid of heat and then the alcohol added ; if this throws down any crystals the solution should be gently warmed, and as soon as clear added to the collo dion. In all cases the solutions should be added in small quantities at a time with constant shaking in between, so as to obtain as fine grained an emulsion as possible.
Silver Bromide Emulsion This was suggested in 1906 by Valenta, and gives an excellent printing-out paper.
A. Celloidin collodion (3 %) . t,000 ccs.
B. Citric acid . . . . 20 g.
Absolute alcohol • . 90 ccs.
Strontium bromide . . 3.2 g.
Glycerine . . . . 4 ccs, C. Silver nitrate . . . 20 g.
Hot distilled water . . so ccs.
Absolute alcohol . . So „ D. Ether. . . . . t6o „ Mix A and B in daylight and add C in the dark room in small quantities with thorough agita tion ; add D, allow the emulsion to stand fifteen minutes, and then filter through wool and use for coating. This gives an extremely rapid printing paper with a long scale of gradation, and therefore requires rather brilliant negatives. An emulsion which is much more suitable for the average negative can be prepared by adding to the B solution : Calcium chloride (anhydrous) . 0•5 g.
Greater contrasts still can be obtained by using uranyl chloride or adding calcium chromate.
Emulsion for Development This gives very slow plates, but the grain is exceptionally fine and very warm tones are obtainable.
Magnesium chloride (crystal) . 4 g.
Absolute alcohol . . . 20 ccs.
Rub up in a mortar, and add— Collodion (z . . . 5o ccs.
As soon as the mixture becomes slimy, add— Ether . . . . . 3o ccs. And finally add Nitro-hydrochloric acid . . 0•6 ccs.
The silver collodion is prepared as follows : Silver nitrate• 4 g.
. .
Hot distilled water . . 3 ccs.
When dissolved, add— Hot alcohol . . . . 20 ccs.
And then— Raw collodion (2 %) . . so ccs.
The chloride collodion should be added to the silver collodion in small quantities, well shaken, and allowed to stand for twenty-four hours with occasional agitation ; then it should be poured in a fine stream into about sixteen times its volume of warm water (mo° F., or nearly 38° C.) with constant stirring. The emulsion is pre cipitated in fine flocks, which should be collected on a clean linen filter, gently squeezed, and then well stirred up with warm water two or three times and finally well drained, rinsing once or twice with alcohol. Five parts of the dried emulsion should be dissolved in ioo parts of a mixture of equal volumes of alcohol and ether, shaken till dissolved, and then filtered.