VARNISHES :- Varnish is a solution of some resinous substance in alcohol, oil or turpentine. The process of covering the surface with varnish is known as varnishing. Varnishing is done only on wooden surface.

Varnish, Types & Application of Varnishes
Varnish application


Function Of varnish:- Varnish performs the Following function
 (i) It brings about brilliance to the painted surface.
(ii) It protects the surface against adverse effects of the atmosphere.
(iii) It increases the durability of the paint film.
(iv) It beautifies the surface without hiding the beautiful grains of the wood.

 Varnish plays an important part in finishing wooden surfaces of doors, windows, floors, furniture, etc.
 Properties of varnishes:-  A good varnish should have the following properties
 (i) It should not hide the natural grains of the surface.
(ii) It should not shrink or show cracks after drying.
(iii) It should make the surface glossy.
(iv) It should dry rapidly.
(v) It should impart the finished surface uniform color and pleasing appearance.
(vi) The thin film of varnish developed after drying on the surface should be tough, hard and durable.
(vii) The natural color of the varnish should not fade away when varnished surface is exposed to atmospheric action.

Constituents of varnish:-
 A varnish has usually three elements
(i) Resins or resinous material
(ii) Driers
(iii) Solvents

 Resins or Resinous Material:-
Quality of varnish depends much upon the quality of resin used. Copal, lac,amber and rosin are the commonly used resins for varnishes. Copal is considered to be best.

 Driers:-  Driers are used to accelerate the process of drying of the varnish. Litharge, lead, acetate, and white copper are the various types of driers, out of which litharge is mostly used.

 Solvents:- A solvent is a substance that dissolve a solute Resulting in solution. It is usually a liquid but can also be a solid, gas, or supercritical form like Acetone, Benene, Alcohol, water....etc

Types of varnish
 The varnishes can be classified into following categories depending upon the  solvent used :
 (i) Oil Varnish
(ii) Spirit Varnish
(iii) Turpentine Varnish
(iv) Water Varnish
(v) Asphalt Varnish
(vi) Spar Varnish
(vii) Flat Varnish

 Oil Varnish:- This type of varnish is manufactured by dissolving hard resins such as amber and copal in linseed oil. Turpentine may be used in small quantity to thin the varnish, and also to render it workable. Oil varnishes form a hard and durable film, but they dry slowly.

 Spirit Varnish:- This type of varnish is prepared by dissolving resins such as lac or shellac in methylated spirit. This varnish dries very quickly and gets easily affected by weather action. This varnish is mostly used for wood furniture.

 Turpentine Varnish:- In this type of varnish, gum, dammar, mastic, and rosin like resins are dissolved in turpentine. These varnishes are light in color and dry quickly.

 Water Varnish:- This varnish is prepared by dissolving shellac in hot water. Shellac does not dissolve readily in water and as such to accelerate the process of dissolving shellac in water either ammonia or potash, or soda or borax is added. This varnish is used for painting pictures, posters and maps.

 Asphalt Varnish:- This varnish is obtained by dissolving melted asphalt in linseed oil. The varnish may be thinned by adding suitable amount of either turpentine or petroleum spirit. This varnish is used for varnishing fabricated iron and steel product.
Spar Varnish:- This varnish derives its name from its use. It is mostly used on spars and other exposed parts of the ships. It is very good weather resistant. It should not be used indoor.
Flat Varnish:- This is an ordinary varnish to which material such as wax, finely divided silica and metallic soaps are added, to reduce the gloss of the varnished This varnish presents a dull appearance.
Process of Application of Varnishes:-
Following operations are required to be carried out while varnishing a wooden surface:

Preparation of Surface:- The surface to be varnished should be thoroughly rubbed smooth by means of sand paper and thoroughly cleaned from dust and dirt.

Knotting:- It is the process by which knots on the surface of wood work are killed by applying certain substance over the knots. All the knots should be covered with a hot preparation of red lead or glue size.

 Stopping:- After knotting, the surface of wood work is stopped by means of hot weak glue size. This coat fills all the pores of the surface. After stopping when surface becomes dry, it is rubbed again with sand paper.

Applying Varnish Coats:- After stopping process, varnish is applied on the surface in very thin coats. Next coat is applied only when previously applied coat has dried. For varnishing, fine brittle varnishing brush should be used.