A Manual Of Photography

THE USE OF ALBUMEN ON GLASS PLATES AND ON PAPER. 277 the thickness of the coating. Or you may arrive at the same result by passing 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 an horizontal posi- tion 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 meist,) 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 develop 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