Spirit Varnishes. The spirit employed for making spirit varnishes • should not be less than 95 per cent. In preparing and using them, they should be kept at a distance from a candle or other flame. Respecting the gums (resins) employed, it may be useful to mention that shellac is rendered more soluble by being powdered and exposed for a long time to the air (see No. 290G); sandarach gives hardness to varnishes; mastich gives a gloss to a solution of other gums; benzoin still more, but its color is objectionable; anime readily dissolves, but renders the varnish long in drying; copal and amber are scarcely soluble in spirit, but are rendered partially so by other gums, and also by being previously fused by heat. (See No. 2SG7.) Shellac gives a durable varnish, objectionable only on account of its color, which may be rendered paler by charcoal. (Beasley.) (See No. 1723 (To Bleach Lac), etc..) In the preparation of spirit varnishes, care should bo taken to prevent the evaporation of the alcohol as much as possible, and also to preserve the portion that evaporates. On the small scale, spirit varnishes are best made by maceration in close bottles. In order to prevent the agglutination of the resin, it is often advantageously mixed with clear silicious sand, or pounded glass, by which the surface is much increased, and the solvent power of the menstruum promoted. The tendency of a spirit varnish to chill or give a rough surface may be destroyed by adding to the varnish a little gum sanda-rach, oil of lavender or concentrated ammonia.

2904. To Dissolve Copal in Spirit

2904.     To Dissolve Copal in Spirit. Take the copal and expose it in a vessel formed like a cullender to the front of a fire, and receive the drops of melted gum in a basin of cold water; then dry them well in a temperature of about 95° Fahr. By treating copal in this way it acquires the property of dissolving in alcohol.

2905. Copal Varnish

2905.    Copal Varnish. Take 1 ounce copal and 1/2 an ounce shellac; powder them well, and put them into a bottle or jar containing 1 quart spirits of wine. Place the mixture in a warm place, and shake it occasionally, until the gums are completely dissolved ; and, when strained, the varnish will be fit for use. The above is the simplest, and therefore the most usual method of making common copal varnish; but it may be prepared in a variety of ways, where particular uses may be required.

2906. To Dissolve Gum Shellac

2906. To Dissolve Gum Shellac. Everybody who has ever to deal with bleached gum shellac knows the difficulties and the loss of time attending its solution. To obviate this, the gum is broken into small pieces and macerated in a stoppered bottle with ether; after swelling up sufficiently, the excess of ether is poured off, when it will dissolve quite readily in alcohol. (See No. 2903.)

2907. Copal Varnish

2907.    Copal Varnish. Take 3 ounces copal, melt by a gentle heat, and drop it into water (see No. 2904 (To Dissolve Copal in Spirit)); then dry it and powder it fine. Place a bottle containing 1 pint oil of turpentine in a water-bath, and add the powdered copal to the turpentine in small portions at a time; in a few days decant the clear. Dries slowly, but is very pale and durable, and is used for pictures, etc.. In making this varnish, it frequently happens that the gum will not melt as readily as it ought, which, in general, is owing to the turpentine not being sufficiently rectified; but, when that is good, it will always succeed. It is best also to let the turpentine be exposed for some time in the sun, in a corked bottle, that the watery particles may be gradually dissipated. The bottle should not be stopped quite tight.