Graduate

A conical-shaped glass with a graduated scale on the side for measuring solutions. Grain.

(a) The texture of dry-plate emulsion, or of sensitized paper.

(b) The unit of English weight. Gramme.

The standard unit of metric measure of weight. It is the weight of a cubic centimeter of distilled water at 32 degrees Fahr.

Grape Sugar. (See Glucose.)

Green Fog

(See Fog, Dichroic.)

Ground-glass

(See Focusing Screen.)

Gum Acacia

(See Gum Arabic.)

Gum Arabic

Gum Acacia. Colorless when pure, but the commercial variety has a yellowish tint. Does not keep well. Dissolves in two parts water. Is insoluble in alcohol. Used as a mountant. Salicylic acid may be used as a preservative. Sometimes employed in gum bichromate process.

Gum Bichromate Process

Similar to the carbon process, in which gum or glue is employed as a vehicle for holding the sensitive materials.

Gum Mastic

Clear, white, or slightly yellow, " tears" about the size of small peas. Soluble in alcohol, ether or chloroform. Used in retouching mediums, etc.

Gum Sandarac

Yellowish crystals. Soluble in alcohol and ether. Used for varnishes, for translucing paper, etc.

Gun Cotton

(See Pyroxylin.)

Gutta Percha

Grayish or yellowish sticks, frequently with reddish-brown streaks; hard, and rather leathery or horny; becomes very soft if placed in boiling water. Only slightly soluble in alcohol, ether and benzine. Used for photographic dishes; also bottles to contain hydrofluoric acid.

Cement for Gutta Percha

Gutta Percha.........................................

2 drms.

Carbon Bisulphide................................

1 oz.

India Rubber.........................................

1 drm.

Fish Glue...............................................

5 drms.

Gypsum

(See Calcium Sulphate.)

Halation

A term used to express the blurred effect which takes the appearance of a halo around brightly lighted portions in a negative, caused by reflections from the back of a glass plate or by lateral spreading of light in the film. The defect is particularly noticeable when brilliantly lighted objects appear quite close to deep shadows. A common example of halation is found when making an interior and a window comes into the view. Both the cause and remedy for halation are thoroughly described in the text of the library, as referred to above.

Half-Plate

English method of denominating a certain size of sensitive plate. The half of a whole plate would be about 6 1/2 x4 1/4, but the standard half plate as used in England, principally, is 6 1/2x4 3/4.