Depending upon the solvent, the varnishes are classified into the following four categories:

(1) Oil varnishes

(2) Spirit varnishes

(3) Turpentine varnishes

(4) Water varnishes.

(I) Oil varnishes: The linseed oil is used as solvent in this type of varnish. The hard resins such as amber and copal are dissolved in linseed oil and if the varnish is not workable, a small quantity of turpentine is added. The oil varnishes dry slowly, but they form hard and durable surface. In fact, these are the hardest and the most suitable varnishes. They are specially adopted for exposed works which require frequent cleaning. They are used on coaches and fittings in houses.

(2) Spirit varnishes: The turpentine spirits of wine are used as solvent in this type of varnish. The resins are of soft variety such as lac or shellac. The spirit varnishes dry quickly: But they are not durable and are easily affected by weathering actions. They are generally used for furniture. The French polish is a variety of this class of varnish and the desired colouring tinge can be obtained by addition of suitable colouring pigment. The French polish is one of the finest finish for ornamental furniture prepared from superior quality of wood.

(3) Turpentine varnishes: The turpentine is used as solvent in this type of varnish. The resins adopted are of soft variety such as gum dammar, mastic and rosin. These varnishes dry quickly and possess light colours. They are not durable and tough as oil varnishes.

(4) Water varnishes: The shellac is dissolved in hot water and enough quantity of either ammonia or borax or borax or potash or soda is added such that shellac is dissolved. These varnishes are used for varnishing maps, pictures, etc. They are also used for delicate internal work and as a covering for wall paper.

Process of varnishing

The application of varnish on the woodwork is carried out in the following way:

(1) Preparation of surface: The woodwork is thoroughly rubbed down by means of sand paper or pumice stone. The surface is then made smooth and clean.

(2) Knotting: The process of knotting is then carried out as in case of painting.

(3) Stopping: The surface of woodwork is then stopped. This is done by means of hot weak glue size. It will fill up the pores on the surface. Ä° N of glue will form about one litre of glue size. Alternatively, the boiled linseed oil can be applied in two costs. When the surface becomes dry, it should be once again rubbed down with sandpaper.

(4) Coats of varnish: The varnish is then applied on the surface in thin coats. The next coat is applied after the previous one has thoroughly dried up. The varnishing should not be done with ordinary paint brushes. But fine haired varnishing brushes should be used.