Amber

The durability of the varnishes is of course mainly dependent upon the comparative insolubility of the resins; their hardness, toughness, and permanence of color. In these respects amber excels all other resins used for varnishes; it resists the action of all ordinary solvents, and can only be dissolved for making varnish by fusion at a high temperature; it is hard and moderately tough, and its color is but little influenced by the atmosphere; but, unless very carefully selected, it is too yellow for delicate works of light colors. Amber is, however, but little in making varnishes, principally on account of its high price, but partly because the varnish dries slowly, and does not attain its full hardness for many weeks.

Amime: is nearly as insoluble and hard as amber, and the best is of a very pale color; but it is not nearly so tough as amber. The varnishes made from anime dry quickly, but are very liable to crack, and the color becomes deeper by exposure to light and air.

Anime is, however, extensively used in making oil varnishes, and most of these called copal varnishes contain a considerable proportion of anime, which is substituted principally on account of its'quick drying qualities.

Copal is next in durability to amber; when very carefully selected it is almost colorless, and becomes rather lighter by exposure; it is more easily dissolved by heat than either amber or anime, and although softer than these resins, is too hard to be scratched by the nail. Copal is, therefore, a most excellent material for varnish, and numerous attempts have been made to employ it as the basis of a spirit varnish, but hitherto with only partial success. Pure alcohol has little effect on copal; with the addition of a small quantity of camphor, the greater portion of the copal is dissolved, but the camphor impairs the durability of the varnish. Copal may be perfectly dissolved by ether, but this spirit evaporates" too rapidly to allow of the varnish being uniformly applied. The essential oils of spruce and lavender have been occasionally employed as solvents of copal, but not with sufficient success to warrant its general adoption in spirit varnishes.

Oil Varnishes

Amber, anime, and copal are usually dissolved for making varnish by fusing the gum, and adding linseed-oil heated nearly to the boiling point. They are then amalgamated by stirring and boiling, and the varnish is reduced to the required degree of fluidity by the addition of oil of turpentine. They constitute the more important of what are called oil varnishes, are the most durable of all, possess considerable brilliancy, and are sufficiently hard to bear polishing. They are therefore employed tor works of the best quality, that are exposed to the weather or to much friction; as coaches, house-decorations, and japanning.

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 naphtha, 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 lackers; 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 quantily 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 tolerable flexible, and may be easily removed by friction with the hand; it is therefore much used for varnishing paintings, and other delicate works.

Da.mar 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.