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Adhesives, Paints, and Varnishes: Asphalt

Asphalt.-Asphalt occurs in nature in veins, beds, and lakes, usually beneath the surface of the ground. In the island of Trinidad, Venezuela, occur lakes of asphalts about three miles in circumference. It is a dry solid with a glossy black surface easily melted and very inflammable. It can be dissolved in alcohol, linseed oil, turpentine, or ether, also in benzol and bisulphide of carbon. With benzol it forms an intensely black solution called black varnish. It is used for varnish, insulation, waterproofing cement, roofing, and painting. Kinds of Varnish. - The character of varnish is largely affected by the substance in which it is dissolved.

Thus we have fixed-oil varnishes in which the principal solvent is turpentine; spirit varnishes or "lac varnishes," true solutions of resins in alcohol, wood spirit, acetone, benzine, etc.; volatile-oil varnishes, the principal solvents being oil of turpentine, and ether varnishes, being solutions of resin in ether. In addition to the above are various special varnishes of gutta percha, wax, and other substances.

FIXED-OIL VARNISHES Solutions of resins in boiled linseed oil have the same durable quality as oil paint, with the addition of a high luster. As in paint, the linseed oil absorbs oxygen from the air, and is converted into a tough, elastic waterproof substance.

To prepare fixed-oil varnishes, melt the resins anime, amber, copal, etc., heat the boiled linseed oil to a high temperature, and pour it into the melted resin in a thin stream, stirring constantly. To test the proper amount of linseed oil to be added to the resin, take out a drop of the fluid now and then and let it cool on a glass plate. When the proportions of oil and resins are correct, the drop will be limpid like wax. If the drop becomes hard and brittle, more oil is required. When mixed, remove from the fire and allow the mixture to cool.

Then dilute to the proper consistency by pouring in turpentine in a thin stream and stirring constantly.

But first boil the mixture of linseed oil and resin before adding the turpentine.

The best quality of linseed oil should be employed for a varnish.

The proper proportions for an ordinary oil varnish are about 10 parts by weight of resin, 5 to 25 parts of boiled linseed oil, and 15 to 25 parts of oil of turpentine. Varnishes of this character usually improve with age. The following are formulas for fixed-oil varnishes:

Amber Varnish.-Eight ounces of amber, 5 ounces of boiled linseed oil, and pint of oil of turpentine. This varnish is very durable, but a slow dryer.

Or, for larger quantities, 6 pounds of amber, 2 gallons of hot linseed oil, and 4 gallons of oil of turpentine.

Melt the amber, add the linseed oil hot, and boil until stringy. Cool and add the turpentine.

Or amber, 16 ounces; boiled linseed oil, 10 ounces; Venetian turpentine or gum lac, 2 ounces; oil of turpentine, 15 or 16 ounces.

Or melt 4 pounds of resin and pound of beeswax. Add 1 gallon of boiled oil at a high temperature. Mix and boil until stringy. Cool and add 2 quarts of turpentine.