<P> Over centuries, many recipes were developed which involved the combination of resins, oils, and other ingredients such as certain waxes . These were believed to impart special tonal qualities to musical instruments and thus were sometimes carefully guarded secrets . The interaction of different ingredients is difficult to predict or reproduce, so expert finishers were often prized professionals . </P> <P> Shellac is a very widely used single - component resin varnish that is alcohol - soluble . It is not used for outdoor surfaces or where it will come into repeated contact with water, such as around a sink or bathtub . The source of shellac resin is a brittle or flaky secretion of the female lac insect, Kerria lacca, found in the forests of Assam and Thailand and harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk . Shellac is the basis of French polish, which for centuries has been the preferred finish for fine furniture . Specified "dewaxed" shellac has been processed to remove the waxy substances from original shellac and can be used as a primer and sanding - sealer substrate for other finishes such as polyurethanes, alkyds, oils, and acrylics . </P> <P> Prepared shellac is typically available in "clear" and "amber" (or "orange") varieties, generally as "three - pound cut" or three pounds dry shellac to one US gallon of alcohol . Other natural color shades such as ruby and yellow are available from specialty pigment or woodworker's supply outlets . Dry shellac is available as refined flakes, "sticklac," "button lac," or "seedlac ." "White pigmented" shellac primer paint is widely available in retail outlets, billed as a fast - drying interior primer "problem solver", in that it adheres to a variety of surfaces and seals off odors and smoke stains . Shellac clean - up may be done either with pure alcohol or with ammonia cleansers . </P> <P> Modern commercially produced varnishes employ some form of alkyd for producing a protective film . Alkyds are chemically modified vegetable oils which operate well in a wide range of conditions and can be engineered to speed up the cure rate and thus harden faster . Better (and more expensive) exterior varnishes employ alkyds made from high performance oils and contain UV - absorbers; this improves gloss - retention and extends the lifetime of the finish . Various resins may also be combined with alkyds as part of the formula for typical "oil" varnishes that are commercially available . </P>

Explain in brief the process of applying varnish and polish on wood