Methods of polishing timber

Following are the ways of conventional varnishing/polishing timber......

1] Oil varnish: Here the resin is copal, a very hard gum, dissolved in a self drying oil like linseed oil. A thinner like benzene or turpentine may be present.  This varnish is slow in drying [may be 24 hours or more] but forms a very hard film and is durable in exterior conditions.  Repeated coats, over a period of time, of this varnish make the wood darker towards black-brown colour.  This was the varnish used in earlier days in India and is still used in Indian villages to protect the wooden trusses, beams, doors, bullock-carts etc.

2] Turpentine varnish:  This is prepared by dissolving soft gums like Rosin in pure turpentine.  Since it dries quickly, a separate drier may not be needed.  However, it does not withstand exterior conditions and hence can be used in interior only.

3] Water varnish: This is prepared by dissolving Lac in hot water along with Ammonia, borax and potash.  This varnish is water resistance on drying and was used in earlier days for laminations on paper.

4] Spirit polish or French polish:  Here the solvent is methyl alcohol and the resin is shellac or lac. These are quick in drying and the film is adequately hard.  It has a bright and glossy finish.  In India, we use this polish for all the furniture.  This polish can be stained with suitable pigments to attain desired colour.  French polish cannot withstand erosion due to direct contact of water. The process of application of this polish is explained later.

5] Lacquer polish: This polish was in use in India and other Asian countries till 1950. But, due to its toxicity, it is becoming obsolete. Shellac, which is a purified extract of lac, is coated on the furniture with or without a soluble oil.  Another accepted version of lacquer-polish is by coating some polymer compounds dissolved in nitrocellulose. The lacquer-polish forms a strong, tough and transparent film on the surface. The film is resistant to water. With the advent of Melamine polish, which is much less toxic than this, this polish is not in use since last 50 years.

6] Melamine polish: Melamine polish is a synthetic resin and hardens when exposed to air. However this hardening is very slow and additional hardeners are added before spraying the coat of this polish. These hardeners, contained in a small bottle, are supplied along with the polish can. Melamine polish is water resistant. It has a better scratch resistance when compared to polishes explained earlier. It is available in mat, semi-gloss and gloss finishes. It is transparent but a faint brown tint is developed. The process of application of this polish is explained later.

7] Polyurethane coat [PU coat]:

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic units joined by urethane (carbamate). The polish-coat of this forms a very strong, protective and glossy film on the wooden surface. Unlike melamine, the drying time for this coat is very short and is around 15 to 30 minutes. This coat is water resistant to a large degree. This polish is more expensive than even melamine polish and costs around Rs. 1200 per Sqm. The process of applying this polish is similar to that of melamine, except for the drying time, and hence is not explained in this chapter later .

            Of these 7 processes briefed above, French polish, melamine polish and polyuretane coat are widely adopted practices in India.