Bronzing

In silver printing, as well as in printing collodion and platinum papers, the hardest or darker portions assume an olive-green color after prolonged exposure. This is called bronzing of the shadows. In the silver papers this disappears on toning, but in the platinum process if bronzing is allowed to go to the extreme the bronzing will appear in the finished print. In the latter case, however, the bronze is overcome by special treatment fully explained in Volume IV.

Bubbles

(See Air-bells.)

Bunsen Burner

A gas jet so constructed that air and the gas mix in such proportions that they burn with a non-luminous flame. The principal advantages are: Small consumption of gas, the great heat it gives out, and the entire freedom from smoke.

Burette

A measuring instrument consisting of a slender tube at the bottom of which is a minute spigot. The tube is graduated so as to divide the fluid into hundredths and thousandths.

Burnisher

A machine for giving a high gloss to photographs by drawing them, under pressure, over a heated nickel-plated roller; also used cold for rolling and flattening prints.

Burnt Sienna

A coloring matter; often used in backing plates to prevent halation.

Bust Portrait

A portrait which shows the head and upper portion of the body of the sitter.

Cabinet

A term generally applied to a special size of picture 3 7/8 x 5 1/2 inches. Of course, it also has the general meaning of a covered or enclosed cabinet in which may be stored various articles, etc.

Cadmium Bromide

CdBr2 - II.

Yellowish, crystal powder. Soluble in alcohol and ether. Used sometimes in the preparation of gelatin plates on account of it being preferable to the other bromides, because of its stability, its solubility in alcohol and ether and its durability.

Cadmium Iodide

Cdl2 - II.

Colorless, flaky crystals. Soluble in water, alcohol or ether. Used as an iodizer for collodion.

Calcium Bromide

Ca Br2.

White granules; very deliquescent; sharp, saline taste. Soluble in water and alcohol. Keep well stoppered. Used in sensitizing solutions.

Calcium Carbide

CaC2.

Grayish-black, irregular lumps. Decomposes with water, evolving acetylene (C2H2) and leaving residue of slacked lime. The acetylene evolved may be taken up by acetone, which will hold 60% of its weight of the gas in solution.

Calcium Carbonate

CaCO3. Precipitated Chalk. Fine, white, amorphous powder. Soluble in acids. Used for neutralizing the gold toning bath.

Calcium Chloride

CaCl2 - V. Muriate of Lime. Pure white, very deliquescent, granular powder, or white, light, easily broken sticks or white lustrous lumps. It absorbs moisture to an enormous degree and, therefore, is used in boxes and tins containing platinum paper in order to keep the paper absolutely dry. When saturated with moisture it may be restored to its full efficiency by placing in a hot oven, then cooled as quickly as possible in a dry place and placed in an air-tight tin.