A Manual Of Photography

THE CALOTYPE. 27 with blotting-paper, and finish drying it at a fire, which will not injure it even if held pretty near: or else it may be left to dry spontaneously. All this is best done in the evening by candle- light : the paper, so far prepared, is called iodized paper, because it has a uniform pale-yellow coating of iodide of silver. It is scarcely sensitive to light, but nevertheless it ought to be kept in a portfolio or drawer until wanted for use. It may be kept for any length of time without spoiling or undergoing any change, if protected from sunshine. When the paper is required for use, talte a sheet of it, and wash it with a liquid prepared in the following manner:— Dissolve 100 grains of crystallised nitrate of silver in two ounces of distilled water ; add to tins solution one-sixth of its volume of strong acetic acid. Let this be called mixture A. Make a saturated solution of crystallised gallic acid in cold dis- tilled water. The quantity dissolved is very small. Call this solution B. Mix together tire liquids A and B in equal volumes, but only a small quantity of them at a time, because the mixture does not keep long without spoiling. This mixture Mr. Talbot calls the gallo-nitrate of silver. This solution must be washed over the iodized paper on the side marked, and being allowed to remain upon it for half a minute, it must be dipped into water, and then lightly dried with blotting-paper. This operation in particular requires the total exclusion of daylight; and although the paper thus prepared has been found to keep for two or three months, it is advisable to use it within a few hours, as it is often rendered useless by spontaneous change in the dark. Paper thus prepared is exquisitely sensitive to light ; an expo- sure of less than a second to diffused daylight being quite sutucient to set up the process of change. If a piece of this paper is partly covered, and the other exposed to daylight for the briefest possible period of time, a very decided impression will be made. This impression is latent and invisible. If, how- ever, the paper be placed aside in the dark, it will gradually develop itself; or it may be brought out immediately by being washed over with the gallo-nitrate of silver, and held at a short distance from the fire, by which the exposed portions become brown, the covered parts remaining of their original colour. The pictures being thus procured, are to be fixed by washing in clean water, and lightly drying between blotting paper, after which they are to be washed over with a solution of bromide of potas- sium, containing 100 grains of that salt, dissolved in eight or ten ounces of water ; after a minute or two, it is again to be dipped into water, and then finally dried.