Science Fair Project Encyclopedia
In a general sense, lacquer is a paint or varnish that produces a hard, durable finish that can be polished to a very high gloss, and gives the illusion of depth. In a narrower sense, lacquer consists of a resin dissolved in a fast-drying solvent which is a mixture of naphtha, xylene, toluene, and ketones, including acetone. The word "lacquer" comes from the lac insect (Laccifer lacca, formerly Coccus lacca), whose secretions have been historically used to make lacquer and shellac.
The earliest known lacquers were made in China and India, perhaps as many as 7,000 years ago. These lacquers, made from urushiol, the sap of the lacquer tree or varnish tree, produce very hard, durable finishes that are both beautiful, and very resistant to damage by water, acid or abrasion. They do not, however, stand up well to ultraviolet light. Urushiol-based lacquers differ from most other lacquers in that they are slow-drying, and dry by oxidation rather than evaporation. Lacquer skills became very highly developed in India and Asia, and many highly decorated pieces were produced.
From China, knowledge of making lacquer ware spread to Korea and Japan. Chinese pieces traveled through various trade routes to the Middle East. Known applications of lacquer in China included coffins, plates, and furniture.
Imitations of Asian and Indian lacquer work became popular in England, France, the Netherlands, and Spain in the 17th century. The European technique, which is used on furniture and other objects, uses varnishes that have a resin base similar to shellac. The technique, which became known as japanning, involves applying several coats of varnish which are each heat-dried and polished.
Quick-drying solvent-based lacquers that contain nitrocellulose, a natural resin obtained from cotton, were developed in the early 1920s, and extensively used in the automobile industry for 30 years. Prior to their introduction, mass produced automotive finishes were limited in color, with Japan Black being the fastest drying and thus most popular. General Motors Oakland automobile brand automobile was the first (1923) to introduce one of the new fast drying nitrocelluous lacquers, a bright blue, produced by DuPont under their Duco tradename.
These lacquers are also used on musical instruments and other objects. The hardened finish dissolves in the solvent, and each coat of lacquer dissolves some of the previous coat. These lacquers were a huge improvement over earlier automobile finishes, both in ease of application, and in color retention. The preferred method of applying quick-drying lacquers is by spraying, and the development of nitrocellulose lacquers led to the first extensive use of spray guns. Nitrocellulose lacquers produce a very hard yet flexible, durable finish that can be polished to a high sheen. Drawback of these lacquers include the hazardous nature of the solvent, which is flammable, volatile and toxic, and the hazards of nitrocellulose, which is also used to make explosives.
Lacquers using acrylic resin, which is synthetic, were developed in the 1950s. Acrylic resin is colourless, transparent thermoplastic, obtained by the polymerization of derivatives of acrylic acid. Acrylic is also used in enamels, which has the advantage of not needing to be buffed to obtain a shine. Enamels, however are slow drying. The advantage of acrylic lacquers, which was recognized by General Motors, is an exceptionally fast drying time. The use of lacquers in automobile finishes was discontinued when the addition catalysts greatly improved the performance of enamels.
Due to health risks involved in the use of solvent-based lacquers, much work has gone in to the development of water-based lacquers. Such lacquers are considerably less toxic and, in many cases, produce acceptable results. More and more water-based colored lacquers are replacing solvent-based colored lacquers in the car industry.
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