Crown Glass

Made the same as ordinary window glass with the exception that greater care is exercised in carefully selecting the various materials for making it.

Flint Glass

Manufactured in a similar manner to other kinds of glass, but possesses a very high refractive and dispersive power.

Jena Glass

So called because it originated in Jena, Prussia. It is especially valuable for the manufacture of high-class lenses, on account of the quality of the various ingredients employed in its manufacture, which render almost any desired degree of refraction or dispersion.

Optical Glass

Made of both flint and crown glass, and lenses constructed of both kinds and placed together overcome chromatic aberration.

Plate Glass

Manufactured by an entirely different process from either crown or flint glass and is especially adapted for use in large windows on account of its strength and toughness.

Ruby Glass

Glass of a reddish or, properly speaking, ruby color. Being a non-actinic medium it is used in the lamp for illuminating the photographic dark-room.

Writing on Glass

When desired to write on glass or place labels upon glass bottles, hydrofluoric acid is generally used. A fine brush dipped in the acid will eat into the glass, leaving an etched surface.

Glucose

C6H13O6.

Dextrose Grape Sugar

White (Anhydrous) powders. A variety of sugar found in the grape and other fruits. Used in some dry-plate emulsions as a preservative and to keep the emulsion moist; also used in silvering glass.

Glue

An impure kind of gelatin. Should not be used for mounting photographs as it is liable to stain the prints.

Glycerine

C3H8O3.

Clear, colorless, syrupy liquid; sweet and warm taste. Used to render gelatin films flexible and flat. Employed for local treatment in development of platinum and bromide prints.

Glycin

C2H5NO2 - II, 524. Glycocoll. A light, lustrous powder. Soluble in water providing the water has been made alkaline. Uses. It is a powerful but slow acting developer. Gives clear images of a grayish-black color. Especially valuable for copying and photomechanical work.

Gold

Au.

A yellowish-brown metal. Toning prints with gold consists of depositing a thin layer of metallic gold on the surface of the print. Gold is used in photography only in conjunction with other chemicals.

Gold Chloride

AuCl3 + HC1 + 4H2O - IV, 51. Gold Trichloride. Yellow crystals. Obtained by dissolving gold in aqua regia (See Aqua Regia). Usually sold in tubes containing 15 grains and is dissolved in 15 drams of water so that each dram of solution contains I grain of gold chloride. Used extensively for toning of silver papers.

Gold Toning

The changing of the color of a printed-out silver print by replacing the silver image with metallic gold - the particles of gold in the bath taking the place of those of silver in the image.