In the Technologist for 1848, M. Niepce de Saint Victor published his mode of applying albumen to glass plates. M. Blan-quart Everard followed; and successively albumen, gelatine, serum, and other animal substances, have been recommended for application on glass : but few of them have been found to answer so perfectly as albumen applied according to the directions of ML Le Gray.
He recommends that the whites of fresh eggs, equal to about five fluid ounces, be mixed with not more than 100 grains of iodide of potassium, and about twenty grains of the bromide, and half that quantity of common salt.
He then directs you to beat this mixture in a large dish with a wooden fork, until it forms a thick white froth ; to let it repose all night, and the next day to decant the viscous liquid which has deposited, and use it for the preparation of your glasses.
For this purpose take thin glass, or, what is much better, ground glass, on which the adherence is more perfect; cut it the size of your camera frame, and grind the edges.
The success of the proof is, in a great measure, due to the evenness of the coat of albumen.
To obtain this, place one of your glasses horizontally, the unpolished side above (if you use ground glass, which I think preferable), and then pour on it an abundant quantity of the albumen. Take a rule of glass, very straight, upon the ends of which have been fastened two bands of stout paper steeped in white wax : hold this with the fingers in such a manner that they will overlap the sides of the glass plate about one-eighth of an inch. You then draw the rule over the glass with one sweep, so as to take off the excess of albumen. The object of the slip of paper is to keep the glass rule from the surface of the plate, and insure a thin but even coating of the albuminous mixture.
Thus, in making the paper band more or less thick, you vary the thickness of the coating. Or you may arrive at the same result by pasting two narrow bands of paper on the sides of the plate, and passing simply the rule down. I prefer the first means, because, with the second, one is almost sure to soil the glass in sticking on the paper.
You must never go the second time over the glass with the rule, or you will make air bubbles. When thus prepared, permit the plate to dry spontaneously, keeping it in a horizontal position and free from dust. When the coat of albumen is well dried, submit your glasses to the temperature of 160° to 180° Fahrenheit; this you may do either before a quick fire, or by shutting them up in an iron saucepan well tinned, with a cover; you then place the saucepan in a bath of boiling water; the action of the heat hardens the albumen; it becomes perfectly insoluble, and ready to receive the aceto-nitrate of silver.
The glass thus prepared may be kept for any length of time. I prepare the first coat also by saturating the former mixture with gallic acid, which gives it more consistency and greater sensitiveness.
When you wish to make a proof (by using the preparation moist), you plunge the glass thus prepared in a bath of aceto-nitrate of silver, described in the second operation of the negative paper. This operation is very delicate, because the least stoppage in its immersion in the bath will operate on the sensitive coating, and cause irregularities which nothing can remedy.
To obtain this instantaneous and regular immersion, I make a box with glass sides, a trifle larger than the plate, and about half an inch wide, with wooden grooves, similar to those in the Daguerreotype plate box : into this I pour the aceto-nitrate, and let the prepared glass fall into it with a single movement, leaving it to soak four or five minutes in the bath ; then remove it, wash well with distilled water, and expose it in the camera while moist. The time will vary from two to thirty minutes, or nearly double that time if the glass is dry.
When you wish to operate with the glasses dry instead of moist, it is proper to dip them in a bath of gallic acid a quarter of an hour after they are taken out of the aceto-nitrate bath; then well wash them with distilled water, and dry them as directed.
When you take the plate out of the camera, you develope the image in the same way as the negative on paper, by putting it into a bath of saturated gallic acid : when it is well developed, fix it by the same method indicated for the paper.
To obtain a positive proof, it is sufficient to apply on the negative proof a sheet of common positive paper, or, better still, a sheet of the positive albuminized paper, which is previously described.
You then put it in the pressure frame, placing above it a piece of black cloth pasted on one side of a thick sheet of glass ; then shut the frame, giving to the proof a slight pressure; after which, expose it to the light. In order to follow its action you may just raise it by one corner of the glass, to judge of the tint which the image takes : when you think it sufficiently exposed, take it out of the frame, and fix it the same as the positive paper.
Niepce de Saint Victor has recently published a process in which he employs starch instead of albumen on the glass plates. The main features of this process are as follows :—About 70 grains of starch are rubbed down with the same quantity of distilled water, and then mixed with three or four ounces more water ; to this is added 5 1/2 grains of iodide of potassium dissolved in a very small quantity of water, and the whole is boiled until the starch is properly dissolved. With this the glass plates are carefully covered, and then placed to dry on a perfectly horizontal table. When thoroughly dried, the aceto-nitrate of silver is applied by wetting a piece of paper, placing this on the starch, and over it another piece of paper wetted with distilled water. This mode of preparation furnishes, it is said, tablets of great sensibility; but the starch is liable to break off from the glass, and there is much difficulty in spreading it uniformly in the first instance.