GUMS AND RESINS The photographer uses gums and resins chiefly in the form of varnishes.
Amber, a fossil resin, ranging in colour from colourless to reddish-brown, is slightly soluble in ether and turpentine ; treated in the same way as copal in varnish making, it dissolves in turpentine, petroleum and benzine.
Anime, or Zanzibar copal, is of two kinds, fossil and " recent," the former being superior ; of pale yellow or yellowish-brown colour and having a rough surface-called " goose skin." It is very hard, and, for varnish making, needs to be treated in the same way as copal ; but it is slightly soluble in ether, benzine, chloroform, cold turpentine, etc.
Copal, a fossil gum, of pale yellow colour, hard and transparent ; soluble slightly in cold tur pentine and fully soluble in turpentine when fused or " run " in a copper pan over a fire, a process that must be left to the varnish manufacturer.
Dammar is known in several forms, ranging in colour from colourless or pale yellow to dark brown and black. It is soluble in oil, ether and benzene.
Dragon's blood is of various kinds, the chief being of blackish-brown colour and being in sticks about t in. thick ; soluble in alcohol, benzene, chloroform, carbon bisulphide, etc.
Elemi is of many kinds and of a white or greyish appearance ; it is soluble in alcohol.
Guaiacum is described under its own heading.
Gum arabic, small rounded nodules of yellow or brownish-yellow colour, is soluble in water but insoluble in alcohol.
Gum benzoin, or gum benjamin, occurring in large blocks of grey or brown colour, with almond shaped particles of a cream colour, is easily pul verised between the fingers, and has a fragrant odour ; soluble in alcohol and slightly so in ether and turpentine.
Gum sandarach, a soft, bright gum, resembles tears or pears in shape, and is semi-transparent ; soluble in alcohol, and slightly so in benzine, petroleum, and turpentine.
Gum tragacanth, or gum dragon, moss-like pieces of whitish colour, is opaque, hard, and tough ; it forms a thick emulsion with water.
Lac is a brown gum, known in many forms— including shellac (shell lac), seed lac, lump lac, stick lac, etc.—which are prepared from a resinous incrustation on the twigs of certain trees. It is soluble in alcohol and ether, and partially so in turpentine. White lac or bleached lac is used in preparing colourless varnish.
Mastic is in the form of tears of a pale yellow colour, brittle, and easily melted ; soluble in alcohol and turpentine. It is used in preparing mastic varnish.
Resin, an amber-coloured or brown oxidation product of turpentine, is brittle, easily melted, of lustrous appearance in a thin coat, and is soluble in alcohol, turpentine, etc.