Spirit Varnishes

Lac and sandarac are more soluble than the above resins, and are generally dissolved in spirits of wine; but sometimes the pyroligneous spirit, commonly known as vegetable naptha, is employed as a cheaper substitute. These resins constitute the basis of what are called spirit varnishes, and are employed principally for delicate objects not exposed to the weather, such as cabinet and painted works.

Lac is much harder and more durable than sandarac, and is the basis of most lackers for hard wood and metal, and also of French polish. Of the three varieties, stick-lac, seed-lac, and shell-lac, the latter is the most free from color, and the most soluble; it is therefore almost exclusively used in making varnishes and lacquers; but the palest shell-lac contains a considerable quantity of coloring matter, that renders it inadmissible for varnishing works of a light color. In addition, shell-lac also contains a small quantity of wax, and other matters, that are only imperfectly soluble in spirits of wine, and therefore give a cloudy appearance to the varnish, but which is not of great importance in varnishing dark-colored works, and may be in great measure avoided by making the solution without heat, and allowing the more insoluble portions time to be precipitated.

Sandarac is softer and less brilliant than shell-lac, but is much lighter in color; it is therefore used for making a pale varnish for light-colored woods, and other works for which the dark color of shell-lac would be unsuited. When hardness is of greater importance than paleness, a portion of shell-lac is added; but when paleness and brilliancy are required, a small quantity of mastic is added. When the varnish is required to be polished, Venice turpentine is added to give sufficient thickness or body.

Mastic is softer than any of the resins previously mentioned, and is dissolved either in spirits of wine or oil of turpentine; the latter is more generally used on account of its cheapness. With either of these solvents mastic makes a varnish of a very pale color, that is brilliant, works easily, and flows better on the surface to which it is applied than most other varnishes. It is also tolerably flexible, and may be easily removed by friction with the hand; it is therefore much used for varnishing paintings, and other delicate works.

Damar is easily dissolved in oil of turpentine, and when carefully selected is almost colorless; it makes a softer varnish than mastic. The two combined, however, form an almost colorless varnish, moderately hard and flexible, and well suited for maps and similar purposes.

Common Resin is generally dissolved either in turpentine or linseed oil with heat. Varnish made with resin is hard and brittle, but brilliant, and is principally employed to make cheap varnishes for common purposes in house-painting, toys, and cabinet work. It is also added to other varnishes in order to improve their brilliancy, but it should be added in small quantities only, as a large proportion of resin renders the varnishes brittle.