The purpose of these varnishes is to protect the metals from oxidation and to render them glossy.

Aluminum Varnish

The following is a process giving a special varnish for aluminum, but it may also be employed for other metals, giving a coating unalterable and indestructible by water or atmospheric influences: Dissolve, preferably in an enameled vessel, 10 parts, by weight, of gum lac in 30 parts of liquid ammonia. Heat on the water bath for about 1 hour and cool. The aluminum to be covered with this varnish is carefully cleaned in potash, and, having applied the varnish, the article is placed in a stove, where it is heated, during a certain time, at a suitable temperature (about 1062° F.).

Brass Varnishes Imitating Gold

I

An excellent gold varnish for brass objects, surgical or optical instruments, etc., is prepared as follows: Gum lac, in grains, pulverized, 30 parts; dragon's blood, 1 part; red sanders wood, 1 part; pounded glass, 10 parts; strong alcohol, 600 parts; after sufficient maceration, filter. The powdered glass simply serves for accelerating the dissolving, by interposing between the particles of gum lac and opal.

II

Reduce to powder, 160 parts, by weight, of turmeric of best quality, and pour over it 2 parts, by weight, of saffron,

and 1,700 parts, by weight, of spirit; digest in a warm place 24 hours, and filter. Next dissolve 80 parts, by weight, of dragon's blood; 80 parts, by weight, of sandarac; 80 parts, by weight, of elemi gum; 50 parts, by weight, of gamboge; 70 parts, by weight, of seedlac. Mix these substances with 250 parts, by weight, of crushed glass, place them in a flask, and pour over this mixture the alcohol colored as above described. Assist the solution by means of a sand or water bath, and filter at the close of the operation. This is a fine varnish for brass scientific instruments.

Bronze Varnishes

I

The following process yields a top varnish for bronze goods and other metallic ware in the most varying shades, the varnish excelling, besides, in high gloss and durability. Fill in a bottle, pale shellac, best quality, 40 parts, by weight; powdered Florentine lake, 12 parts, by weight; gamboge, 30 parts, by weight; dragon's blood, also powdered, 6 parts, by weight; and add 400 parts, by weight, of spirit of wine. This mixture is allowed to dissolve, the best way being to heat the bottle on the water bath until the boiling point of water is almost reached, shaking from time to time until all is dissolved. Upon cooling, decant the liquid, which constitutes a varnish of dark-red color, from any sediment that may be present. In a second bottle dissolve in the same manner 24 parts, by weight, of gamboge in 400 parts, by weight, of spirit of wine, from which will result a varnish of golden-yellow tint. According to the hue desired, mix the red varnish with the yellow variety, producing in this way any shade from the deepest red to the color of gold. If required, dilute with spirit of wine. The application of the varnish should be conducted as usual, that is, the article should be slightly warm, it being necessary to adhere strictly to a certain temperature, which can be easily determined by trials and maintained by experience. In order to give this varnish a pale-yellow to greenish-yellow tone, mix 10 drops of picric acid with about 3 parts, by weight, of spirit of wine, and add to a small quantity of the varnish some of this mixture until the desired shade has been reached. Picric acid is poisonous, and the keeping of varnish mixed with this acid in a closed bottle is not advisable, because there is danger of an explosion. Therefore, it is best to prepare only so much varnish at one time as is necessary for the immediate purpose.