Home › Photography › Glass for Photography

Glass for Photography

For in a room of evenly diffused light the iodide portraiture and ordinary landscape photo- of cadmium as the principal excitant gives graphy, the best qualities of picture or win- softness and delicacy to the image. Thus: dow glass will suffice. There is an article I. Take of sulphuric ether, 1 ounce; 95 per sold by dealers in photographic materials, cent. alcohol, 1 ounce; gun cotton, 6 grains; known as photographic or negative glass, iodide of cadmium, 4 grains; bromide of cadwhich is selected for the purpose and cut into mium, 2 grains. the regular sizes used in the art, viz., stereoscopic, "quarter" size, "half" size, "fourfour" &c., the latter being 6×84 inches and the other sizes fractional parts, as their names suggest. For microscopic and scientific experiments, plate glass would be preferable. A quality known as "three quarter white" plate, and only of the thickness of ordinary single thick window glass, has all the requisites for exact photography. When it is proposed to print photographs upon glass, for magic lanterns or transparencies, plate glass is absolutely essential. 3148. To Prepare Glass for Photography. All new glass should be placed for a few minutes in a strong solution of commercial nitric acid (say 1 ounce nitric acid to 3 ounces water), and then thoroughly washed in clean water. While wet, pour upon the glass a solution consisting of white of egg, 1 ounce; water, 20 ounces; drain off into a These two formulæ give the utmost delicacy and transparency to the shadows, and work with rapidity, when preserving their proper relations to the silver bath solution, of which we speak in the proper place. If more brightness is desired to the image, instead of the iodide of cadmium put the same quantity of iodide of ammonium. If still greater contrasts are required, use iodide of potassium in place of either the cadmium or potassium.

The latter is favorable for copying engravings, maps, plans, &c., in which strong contrasts of white and black are desirable. It is well to prepare from all these formulæ and then modify results by mixing them together as the subjects or light may demand. Farther combinations may be suggested; under a separate bottle, or clean, filter, and set up in a feeble light, or where there are large masses of rack to dry. The albumen and water solution, shadow, reduce the amount of the iodide salt before using, should be very thoroughly beaten one grain and increase the bromide one grain. IN COMBINING THE INGREDIENTS, measure with normal collodion of the usual descripout the required quantity of alcohol, and to tion, and when the film has set perfectly, but it add the gun cotton and such of the exciting has not become completely dry, the pictures, salts as dissolve in alcohol, and lastly the which have previously been trimmed and ether. Shake until all are thoroughly dis- finished, are dipped rapidly into alcohol, and solved, and put aside over night to settle. applied without delay to the plates. The When clear, decant into the flowing or coating prints are pressed and rubbed down with bottle for use. Such of the excitants as do smooth writing paper, and the operation of not dissolve in alcohol should be dissolved in mounting is proceeded with as soon as the as small a quantity of water as is possible and backs of the pictures have become white; or, added to the alcohol, &c., a little at a time, and in other words, as soon as the alcohol has quickly shaken. again evaporated. The cardboard should be