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Albumen

water, plates, solution, bath, toning, dissolved, acid, grains, plate and placed

ALBUMEN PROCESS.—The albumen glass positive process is still much used for making transparencies, lantern and stereoscopic slides. The manipulations may be carried on in a yellow light, it being more pleasant to work in than the red. First prepare a solution of albumen by breaking up eggs separately and removing the yolks. When 12 ounces of the whites have been collected, place in a convenient vessel and add half a drachm of glacial acetic acid diluted in one ounce of water. Stir it well with the albumen with a glass rod for about two minutes, a little care being taken that froth is not produced. The addition of the acetic acid causes a flocculent deposit, which in about an hour collects itself in a mass at the top of the solution. This is easily removed with pieces of paper, and the albumen should be perfectly clear and rather limpid. Strain through linen and add 5o minims of ammonia sp. gr. .88o to restore the viscidity destroyed by the acid. The next addition is one drachm of ammonium iodide and eight grains ammonium bromide. When these ingredients are dissolved, the albumen is ready for use at any time if kept in well-corked bottles, remaining good for at least a year.

We must next select the glass. If for lantern slides it must, of course, be of a better quality, and free from bubbles or other impurities. This is coated with a plain collodion, and as soon as the film has set the whole is plunged in a dish of cold water, where it is allowed to remain from four to five minutes. Each glass so coated and treated is next rinsed under a tap to remove all apparent greasiness, and then stood up on end on a pad of blotting paper.

The albumen is next filtered through cotton wool (a small tuft being placed in the neck of a funnel) into a glass measure. A little of it is then poured on the upper end of the plate and made to flow over the whole of the film in one continuous wave, driving the water before it off the plate into the sink, and following it itself. Drain the plate well, and then pour on a fresh portion of the albumen, and let it flow backward and forward to allow it to soak well into the porous collodion film ; then drain it off into a measure and place the plate carefully in a rack. Coat as many as will be required for some time, as they will keep for a lengthy period. The rack containing the plates should be placed in a warm room to allow them to dry, and as soon as they dry they are placed before a fire and made as hot as the hand can possibly bear. The object of this is to prevent the film blistering during the subsequent treatment, and it is a very effective means. The plates have next to be sensitized. In one pint of distilled water dissolve four grains of potassium iodide and add 2 ounces of silver nitrate. When this has dissolved, add ounces of glacial acetic acid, and the sensitizing bath is ready for use. The plates can be laid in a dish containing the solution, but, if possible, use a dipping bath, as described in the wet collodion manipulations. The time of immersion should not exceed half or three-quarters of a

minute. When taking from the sensitizing bath the plates are placed in a dish of distilled water to remove the free silver nitrate. They are then well rinsed under a tap and again placed in the drying rack. These sensitized plates may be made to keep if treated with a solution of gallic acid. If the sensitizing bath becomes discolored, as it will do if many plates are prepared in it, shake up a little kaolin in it, and the discoloration will disappear, and the bath resume its pristine efficacy.

Printing is usually done by superposition. The exposure differs, of course, with the quality of the negative and the light. A negative of medium density will require, at one foot from an ordinary fish-tail gas burner, an exposure of between ten to twenty seconds. Practice alone enables one to judge correctly, and with plates of this description there is a great latitude.

For development, prepare two solutions, the first containing three grains of pyrogallic acid dissolved in one ounce of water ; and the second five grains of silver nitrate and five grains of citric acid dissolved in one ounce of distilled water. Label these r and 2 respectively. First flood the plate with water containing a few drops of Solution 2 until the film is thoroughly permeated. Pour it away and replace by Solution r, to each ounce of which four drops of Solution 2 have been added. In about a minute the image should make its appearance. When all the details are visible, pour the developer into a measure and add to each ounce half a drachm of Solution 2. Mix, and pour on and off the plate until the image has attained the requisite density. This should, however, be very slight, as the color is obtained in the toning.

The toning bath consists of two ounces of sodium hyposulphite dissolved in eight ounces of water, and when dissolved, four grains of gold chloride added gradually, stirring rapidly the while. The addition of 30 grains of silver nitrate dissolved in an ounce of water has been recommended as improving the color obtained in toning. After mixing the toning bath it must be allowed to stand for at least 12 hours. In toning, the plates are placed in a dish, and the solution poured over them. The process is a very slow one • half an hour is sometimes required to obtain a rich black tone. In regulating the density of the toning it is necessary to remember that the pictures appear much denser when dry than when wet. The toning bath will keep for any length of time ; it improves, in fact, by keeping, and when inclined to be weak add a little more gold. This must be done, however, io or 12 hours before using. When the desired tone has been attained, the plates are well rinsed under the tap, and afterward left to soak for a little time in several changes of water to thoroughly eliminate the hypo from the film.

Albumen transparencies should not be varnished, but mounted with a protecting glass.