Copper Sulphate

CuSO4 + 5H2O - II.

Copperas; Blue Stone; Cupric Sulphate; Blue Vitriol

Large, deep-blue crystals, slowly efflorescent in dry air; stringent, metallic, styptic taste. Soluble in 2.6 parts water. Used to bleach untoned prints or bromides when desired to sketch over with India ink for line reproduction; also, used in conjunction with other chemicals for toning bromide prints.


Term applied to making copies.

Corrosive Sublimate

(See Mercuric Chloride.)

Gun Cotton

(See Pyroxyline.)

Cotton Wool

Raw Cotton


A plain glass used to protect the film side of a lantern-slide.

Covering Power

(See Lens, Covering Power.)

Cracked Negatives

X. Cramer Plates - II, 551-641.

Crookes' Tube

A large vacuum tube, spherical or pear-shaped, used in conjunction with a powerful induction coil to produce Rontgen, or X-rays.

Crown Glass

(See Glass, Crown.)


An earthenware vessel made to withstand very high temperatures. Used for melting or fusing various metals and chemicals.


An inorganic substance which has assumed the form of a regular solid, commonly bounded by plane surfaces. Crystals of various substances may be formed by dissolving or by fusing, and allowing to cool gradually.


The process of becoming crystalized.

Crystal Markings

The formation of crystals on the surface of the negative due to improperly washing after fixing.

Cupric Sulphate

(See Copper Sulphate.)

Curvature of Field

An optical term used to denote the effect produced by a lens, the field of which is spherical in shape rather than plane. In other words, the focus of the central rays of light on a plane farther from the lens than that of the marginal rays.

Cut-out Forms

Sheets of brass, celluloid or other material, having openings of various sizes and shapes for the trimming of prints by means of a small cutting wheel.

Cutting Plates

(See Plates, Cutting.)

Cyanide of Potassium

(See Potassium Cyanide.)

Dagor Lens

(See Lens, Dagor.)


One of the first photographic processes. The picture is obtained on a highly polished silver plate. With this process a direct positive is obtained, the plate being sensitized by exposure to fumes of iodine in a dark box. After exposure in the camera, the latent image is developed by fumes of mercury and fixed by hypo and sulphite of soda. The process is named after the inventor, Daguerre, and was first successful in 1839.

Dallmeyer Lens

(See Lens, Dallmeyer.)


Dammar. Yellowish-white, roundish, semi-transparent masses of varying degrees of hardness. Soluble in oil of turpentine, benzole or chloroform. Used in varnishes and retouching mediums.