The term varnish is used to designate any solution, which, when spread with a brush in a thin layer on the surface of an object, dries with a smooth, lustrous, transparent film.

The principal ingredients used are gum resins, linseed oil, turpentine, benzine and suitable dryers for oil varnishes; and gums, resins and alcohol for spirit varnishes; the latter, as a rule, are simple solutions of gum in spirits, and while quick drying and of fair utility, are necessarily brittle and not able to stand wear and tear.

When gums or resins are dissolved by the aid of heat with the addition of prepared or boiled linseed oil, and thinned with turpentine or benzine to the proper consistency, we have, in a general way, defined oil varnishes, which, because of the oil entering into their composition, have added elasticity and increased durability over spirit varnishes.

Two essentials are needed to produce good varnishes; suitable materials of good quality and skill in making, to adapt the varnish to the purpose for which it is intended.

The gums or resins in common use are known as Zanzibar, angola, sierra leone, benguela, kauri, manilla, damar, (both Batavian and Singapore) shellac and rosin.

Zanzibar, kauri, and manilla copals enter into the great bulk of the oil varnishes, except the cheaper grades which are made from rosin.

Zanzibar and other copal gums, as well as kauri are fossil or semi-fossil resins, which had their origin in resin producing trees long extinct. These gums, having been in the ground, hardened in the course of time. The same gums are still being produced from similar species of trees in the various localities from whence the fossil varieties are obtained.

Manilla copals come from several species of trees growing in the Philippines, the principal source being from the Bread tree. Varieties are also met with in Mexico and Brazil. This gum resin is soft, in fact few degrees removed from ordinary rosin save from the fact that it has some elasticity.

Batavia and Singapore demars are soft gums, used mainly because of their transparency and absence of color. The first is from the East Indies and the Phillipines, produced by the Amboyna pine tree, while Singapore demar comes from a somewhat different species of tree which grows in British India and the islands before mentioned.

Shellac comes from southern Asia and the East Indies. It is produced by an insect which lives on several varieties of trees and shrubs.

These insects puncture the trees and are covered by the exuding juices. The formation due to these burrowings is reddish brown in color and consists of coloring matter, wax and resin. This is crude shellac. The best qualities are those collected before the insects have escaped from their envelopment. The crude product is termed stick lac, being the crude shellac adhering to the twigs and branches on which it is formed.

The product is ground, cleaned and treated with weak caustic soda and then with alum which removes some of the coloring matter. It is then dried, melted, run into heated flat moulds, taken from thence hot, and spread over a hollow cylinder filled with warm water. The layer formed is smoothed, detached and dried in an airy place. It is a very brittle substance, softens with heat, and is inflammable. It is partially soluble in alcohol and fully so in alkalies and borax solutions. Shellac is marketed as stick lac, which is the crude shellac adhering to the twigs on which it was formed, button lac or melted shellac, free from woody fibre and other foreign matter, and the various grades of refined shellac. Of the latter, there are two principal divisions; the so-called native shellacs, prepared by crude methods, and characterized by their dark color and slight impurity, and the carefully treated shellacs graded according to quality under various brands ranging in color from pale orange to light brown. White, or bleached shellac is made by several processes. In a general way the treatment is as follows: The shellac is dissolved in a solution of carbonate of soda or other alkali, a certain proportion of chloride of lime is added, and, after standing a day or two, the gum is precipitated with hydrochloric acid, washed and dried.

Shellac is used largely in spirit varnishes and in the preparation of shellac japans. It is used for various purposes in the arts also.

Asphaltum, the base of most black varnishes, is a black pitch-like substance, found as a natural deposit in many localities throughout the world. It varies much in hardness, color and elasticity. A pitch of similar nature is left as a residue in the distillation of coal tar and from some kinds of crude petroleum. The hard asphaltums, because of their brittleness, make less durable varnishes unless a sufficient amount of linseed oil is added.

Certain cheap black varnishes are made by simply melting cheap grades of asphaltum and reducing the product with benzine. During the process of melting some black manganese is added as a dryer.

Rosin is produced as before mentioned, in the manufacture of turpentine.

Two other gums are used in spirit varnishes; mastic and sandarac. The best quality of mastic is produced by a tree of the cashew-nut order, growing in the islands of Greece. The rosin exudes from the bark where cut, in the form of tears. It has a pale yellow color and is brittle and fragile.

Sandarac is a pale yellow resin, produced by a conifer growing in Algiers. It is soft and brittle, somewhat like mastic. These gum resins are used in certain lacquers, but mainly in spirit varnishes prepared and used by artists.

The better grades of varnishes are made almost wholly from Zanzibar and kauri gums, because of the hardness and durability of these resins. While not so hard as some others, kauri gum in particular, is easily worked and free from the objections found in many others.

Carriage varnishes, exterior finishes and the better interior varnishes contain these gums. Manilla copals are used mainly in the medium and cheaper grades for interior use. Damar varnish is usually a simple solution of the resin in turpentine or benzine prepared with or without the aid of heat. The cheaper grades of demar varnish are largely adulterated with white rosin which is easily-dissolved in the same solvents.