Based on the solvent used, varnishes may be classified as given below:
1. Oil Varnishes
Oil varnishes are prepared from the hardest resin or gums, such as amba, copal, etc., by heating and dissolving them in linseed oil with turpentine. Heat is added to increase the workability. Although it dries slowly, it is the hardest and most durable of all varnishes. In general, it can be used both for interior and exterior works. It is preferred for joinery and fitting purposes and for all outside works.
2. Turpentine Varnishes
These varnishes are prepared from soft resins such as gum dammar, mastic, common resins, etc., by dissolving them in pure spirits or turpentine. These varnishes are flexible, lighter in colour and quick in drying. Compared to oil varnishes they are weak.
3. Spirit Varnishes
These varnishes are also called lacquers. These are prepared from soft resins such as lac or shellac dissolved in methylated spirit. They are harder, dries quickly and brilliant in appearance. These are easily affected by weathering actions.
4. Water Varnishes
These varnishes are prepared using shellac, which is dissolved in hot water and mixed with an adequate quantity of ammonia or borax, potash or soda such that the shellac gets dissolved. Water varnishes are used to varnish wallpapers, maps, pictures, etc.
5. French Polish
This is a refined spirit varnish. It is prepared by dissolving 0.15 kg of black or light brown shellac in one litre of methylated spirit without heat. The polish is obtained by adding a suitable colour pigment. This polish dries out quickly within a few minutes. It gives a fine glossy surface. It is mostly used for superior wood works like furniture, hand rails, etc.
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