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Tannin

plate, solution, water and add

TANNIN PROCESS.—An old dry-collodion process invented by Major Russell. A glass plate is first well cleaned with Tripoli powder, and then washed in clean water and dried with a soft cloth previously warmed. One side of the plate is then coated with the following gelatine solution in the same manner as collodion : Dissolve the gelatine in the water and add the spirits of wine. The solution is then filtered through fine muslin or flannel.

After coating the plate with this the superfluous gelatine is poured back into the bottle, and the plate stood up on end on a piece of blotting paper, to drain and dry. When dry it is slightly warmed, and can then be packed away in a grooved box. A number of plates can thus be coated at one time, as, if they are carefully packed, they will keep any length of time. Care must be taken in coating that none of the gelatine solution gets on to the back of the plate. They are next coated with an old iodized collodion in the usual way, and then placed in a similar nitrate of silver bath to that used in the old wet-collodion process. In this bath the plate is allowed to remain for about five minutes, when it is taken out and well washed with plenty of water.

The tannin preservative bath is prepared as follows : To every ounce of distilled water required in the bath add 15 grains of tannin. Filter and pour out two separate portions of about four drachms each, one to be used for the first coating of the plate, which serves to remove the water remaining upon it after washing, and the second portion is then poured on and off the sen sitized side of the plate. This operation is repeated several times, and the plate is then stood in

a warm and dark room, resting upon blotting paper, and when dry it is ready for use in the camera. The time necessary for exposure usually varies between one minute on a favorable day to eight minutes in dull and dark weather.

The developing solution is made up as follows : Filter. For use, add half a drachm of No. i Solution to 3 ounces of distilled water, and then take about 3 drachms of this diluted pyro solution, and add to it from io to 15 minims of the silver nitrate and acid solution. Moisten the exposed plate with water, quickly and evenly applied, then pour on the developing solution, and let it flow gently to and fro over the plate. If the sky comes out quickly and strongly, but the details do not, it is a proof of under-exposure, which can sometimes be remedied by the addition of a little more pyro to the developer. If, however, the image appears to come out suddenly, the plate has no doubt been over-exposed; it is then neces sary to add a few drops of Solution No. 2 to the developer. After development the plate is fixed with sodium hyposulphite, well washed, dried, and varnished.