The first formula was Simpson's, and, although old, it can be made to yield really good pictures. To each ounce of methylated spirit i6 grains of silver nitrate are added by triturating the salt in a mortar, then adding the spirit a little at a time and pouring it off until it is dissolved. A stock solution can be made, and to each ounce of it one ounce of ether is added and the necessary proportion of soluble gun-cotton. The proportion of cotton depends much upon its quality; of some samples six grains to the ounce gives a collodion quite thick enough, and with some other kinds ten or twelve grains to the ounce may be required.
After the collodion is formed the addition of three-quarters of a drachm of a solution of chloride of calcium or alcohol, 16 grains to the ounce is made. This is added a drop at a time, the collodion being shaken between each addition. The sensitive emulsion ready for use is thus formed.
Liesegang's formula is one that has given very satisfactory results in our hands- In a glass measure dissolve 8 grammes of nitrate of silver in 6 c.c. of distilled water, heat being applied. Drop this solution in a bottle containing x35 c.c. of alcohol. In cool weather it is necessary to place the bottle in a vessel containing warm water, add 8 grammes of soluble gun-cotton, and after a good shaking pour in i6o c.c. of ether. Further violent shaking will produce a grayish white collodion. In another glass dissolve x gramme of chloride of lithium in 35 c.c. of alcohol, together with z gramme of tartaric acid. This solution is dropped into the argentiferous collodion, which must be kept continually moving. For vigorous negatives take more of the chloride, as softer prints result from doing so. If preserved in a well-corked bottle this collodion will keep any length of time.
Heiderstadt's formula is as follows: 1.5 gramme of chloride of lithium, 1.5 gramme of nitric acid are dissolved by the application of heat in 5o c.c. of alcohol; this solution is added to 500 grammes of ordinary 4 per cent. collodion. x4 grains of acetate of silver are dissolved with the aid of heat in 6.7 grammes of distilled water, then added to 15o c.c. of diluted alcohol, which is heated to ebullition. The argentiferous solution is poured gradually into the chloride solution, and afterwards from 4 tc 6 grains of glycerine solution added.
In the Deutsche Photo Zeitung, Herr Vollenbruch published the following process for the preparation of a collodion paper. The emulsion contains the following ingredients: Strontium chloride. 4 grammes 6x .7 grains Lithium chloride . 2 grammes 30.8 grains Citric acid. 8 grammes 123.4 grains Glycerine, pure 12-14 C.C111 210 minims
Silver nitrate.... ........ 28 grammes 432 grains Ether . zoo c.cm. 27 fluid drachms Alcohol too c. cm . 27 fluid drachms Collodion 3 per cent. pyroxline..80o c.cm 216 fluid drachms It is prepared thus: A. Dissolve the silver in 13o minims of water, then add 13j4 drachms of alcohol, and mix it to half the quantity of collodion ( xo8 drachms).
B. Dissolve the strontium and lithium chloride in z36 drachms of water, add 63 drachms of alcohol, and finally mix the whole to the remainder of collodion.
Now mix gradually, in shaking, meanwhile, B to A, and when the emulsion is made, add the ether and the glycerine. Allow it to stand for a few hours, filter and use. This quantity of emulsion is sufficient to coat from thirty to thirty-five sheets of paper 10 x 23 inches.
Preparation of the are two ways of preparing the emulsion, one in which plain, ready-made collodion is used and the silver and salts added to it, and the other in which the collodion is made in the same process. We will give them both.
For the first method we require a plain collodion. This can be purchased or prepared by mixing equal parts of ether and alcohol, and adding 2 to 3 per cent. of English pyroxyline. Now the thickness of the collodion is a very important matter. We would recommend a 2 per cent. in the summer and a 3 per cent. in the winter; a thin collodion is always better to work with; it gives an evener film, and if sufficient density is lacking, it is a very simple matter to coat the paper a second time, or it can be allowed to remain longer on the paper before pouring off the superfluous quantity. If, however, a thick collodion is used all manner of evils arise. The film is likely to be thicker in some parts than in others, which would be at once seen in the toning, as the thinner parts would soon become acted upon by the gold bath leaving the thicker portions quite red.
Collodion, like wine, improves by keeping. An old collodion that has been allowed to stand some time is always superior to one freshly made, for the reason that it is more perfectly combined and, all sediment and foreign matter having fallen to the bottom, it is much clearer and cleaner. Therefore, it is advisable to make the collodion some time previous to use. Keep it in a properly shaped collodion bottle (see Fig. 13o), and, after carefully decanting it without disturbing the sediment at the bottom, add about one-half per cent. of castor oil. The addition of this small quantity of castor oil makes a wonderful difference in the glaze of the finished picture, while materially assisting the toning.