Piano finishes, too, have changed much over the years. The traditional piano finishes in the 18th and 19th centuries were shellac and varnish. Shellac, made from insect shells dissolved in alcohol, is a relatively nontoxic finish that, when damaged, is easily repaired. It is, however, difficult and time consuming to apply evenly in large quantities, and its highest expression, French polish, requires great skill.
Varnishes are made of various kinds of resins dissolved in oils such as mineral spirits. Exposed to light, varnish tends to darken and wrinkle as it ages, creating the "alligatored" appearance so often seen on early 20th-century pianos. A beautiful and durable coating, varnish was the piano finish of choice from the late 19th century until the development of cellulose lacquer in 1928. Lacquer, essentially a synthetic shellac made of cellulose dissolved in volatile solvents such as acetone, can be sprayed on and dries faster than varnish, which makes it attractive for use in a factory setting — but it is highly toxic.
In the mid-20th century, chemists developed polyurethane varnishes and polyester wood finishes. Polyurethane, a kind of synthetic varnish, is used on some pianos to create a satin finish. Polyester, basically a plastic, has become very popular, and is very likely to be the shiny, deep finish you see on new instruments. The hardest piano finish, polyester is extremely toxic in its liquid form, but is resistant to pretty much everything a piano might normally be exposed to, including water, alcohol, and scratching.
Plastic in the Action
All of this leads up to what may well be the most dramatic use of nontraditional materials in piano construction since the development of the modern piano in the last half of the 19th century. A few piano manufacturers, most notably Kawai and Mason & Hamlin, have invested heavily in research and development to design and produce plastic action parts for their pianos. Contrary to what one might think, the goal is not to save money, as both the research and development expenses and the cost of producing the parts are substantial. According to Bruce Clark, senior design engineer at Mason & Hamlin and its subsidiary piano-action company, Wessell, Nickel & Gross (WNG), "The only reason you do this is to make better parts. In 1850 wood was the high-tech best material for piano actions; that's no longer true."