ALBUMEN-NEGATIVE PROCESS ON GLASS.
, To prepare the Abumen.—Colleet in a basin the whites of a number of eggs, carefully separating the germ, and all portions of yelk. To each ounce of this albumen add one dram of distilled water, in which is dissolved 6 grains of iodide of potassium ; also to every 5 ounce,s of the mixture add one drop of ammonia. Beat the whole to a stiff froth with a bunch of and allow the liquid to settle till the following day.
To albumenize the Plate.—The glass plate must first be deaned very thoroughly, and polished .with a cambric handkerchief just before use. (On this head see the article " Cleaning.") Attach to the under side of it a gutta percha plate-holder, having a wooden handle a foot long. Then breathe on the plate, and, holding it horizontally in the left hand, pour upon the centre of it a sufficient quantity of the albumen from the basin to cover it, allowing the albumen to filter through an opening in the dry froth or crust. Make the albumen flow backwards and forwards over the plate three or four times, and then let it all run off into a separate basin, from which it must be carefully filtered before being used a second time. Tn coatin,g the plate, be particularly careful to prevent air-bubbles from forming upon it. Next, take the handle of the plate-holder between your hands, and, with the plate in a vertical position, spin it round quickly for a minute or so, in order to drive the albumen to the edges by centrifugal force. This done, remove the excess of albumen from the edges by means of a pipette (see "Pipette"), and dry the plate before a clear fire, keeping it rotating all the time by means of the handle, as before directed. When dry it is ready for the next operation. Albumenized plates may be put away in a plate box, and kept for a considerable time without deterioration in a dry place. Care must be taken, in the operation of albumenizing the plate, that no particles of dust adhere to it.
To excite th.e Plate.—Place it on a dipper, and immerse it quickly and without hesitation in a vertical bath of aceto-nitrate of silver, made thus : Distilled water 1 ounce, nitrate of silver 50 grains, glacial acetic acid 1 dram. Leave it in the bath for a couple of minutes, then wash it well in clean water, and lastly in distilled water, and set it up to dry. When dry put it away in the plate-box until ready for use in the camera. It may be preserved in a sensitive state for several days. Some persons add a few drops of a solution of iodide of potassium to a new nitrate bath, and filter it on the following day, in order to saturate it with iodide of silver. When this is done a new bath is not so liable to attack the iodide of silver in the film.
The Exposure.—Albumenized plates, from which the excess of free nitrate of silver has been removed by washine, are, whether used in a dry or wet state, extremely insensitive to li;ht ; but, when only slightly washed, exposed at once, and developed with a strong developer, a much shorter exposure is sufficient. This should be timed solely with reference to the shadows, the lights being left to _take care of themselves. When the camera is properly constructed, to prevent stray light from falling on the plate, it is hardly to over-expose a dry, washed, albumenized plate.
To develop the Image.—First, immerse the plate in distilled water ; then place it in a levelling-stand, and pour over it a saturated solution of genic acid, to which a few drops of aceto-nitrate of silver have been added. The development occupies about twenty minutes.
To fix the Picture.—Wash the plate in rain water, and pour over it a nearly saturated solution of hyposulphite of soda. This will quickly remove the yellow iodide of silver from the film. Then wash the plate well under a tap, and dry it before the fire.
The negative may be varnished with any good varnish, (see "Var nish,") but this is not always done.