Lacquer

In a general sense, lacquer is a clear or colored coating, that dries by solvent evaporation only and 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.

Lacquer box with children, from Qianlong period, Qing Dynasty, 1736-1795, from National Museum of China, Beijing, PRC. Photo by Andrew Lih.

Urushiol-based lacquers

The earliest known lacquers were made in China and India, perhaps as many as 7,000 years ago. These lacquers, the resin of trees Rhus verniciflua or Toxicodendron verniciflua, 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, water based, and set by oxidation and polymerisation, rather than by evaporation alone. The active ingredient of the resin is urushiol, a mixture of various phenols suspended in water, plus a few proteins. The phenols oxidize and polymerize under the action of an enzyyme laccase, yielding a substrate that, upon proper evaporation of its water content, is hard and fairly resistant to mechanical stress. 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, music instruments and furniture.

Japanning

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.

Nitrocellulose lacquers

Quick-drying solvent-based lacquers that contain nitrocellulose, a resin obtained from the nitration of cotton other cellulostic materials, 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 wooden products, furniture primarily, and on musical instruments and other objects. The nitrocellulose and other reins and plasticizers are dissolved in the solvent, and each coat of lacquer dissolves some of the previous coat. These lacquers were a huge improvement over earlier automobile and furniture 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 handling hazards of nitrocellulose in the lacquer manufacturing process. Lacquer grade or soluble nitrocellulose is closely related to the more highly nitrated form which is used to make explosives.

Acrylic lacquers

Lacquers using acrylic resin, a synthetic polymer, 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 have 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 tougher, more durable, weather and chemical resistant two-component polyurethane coatings were developed. The system usually consists of a primer, color coat and clear topcoat, commonly known as clear coat finishes.

Water-based lacquers

Due to health risks and environmental considerations 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 more environmentally friendly, and in many cases, produce acceptable results. More and more water-based colored lacquers are replacing solvent-based clear and colored lacquers in underhood and interior applications in the automobile and other similar industrial applications. Water based laquers are used extensively in wood furniture finishing as well.

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