Lacquer and its sources
The best known lacquer, sometimes called 'true' lacquer, is an urushiol-based lacquer common in East Asia. It is obtained from the dried sap of the lacquer tree, Toxicodendron vernicifluum. Other types of lacquers are processed from a variety of plants and insects. Attempts to imitate the 'true' lacquer of East Asia, such as Japanning in Europe, are often loosely called imitation lacquer.
Urushi
Toxicodendron vernicifluum is an Asian tree species native to China and the Indian subcontinent, and cultivated in regions of China, Japan and Korea. The tree is cultivated and tapped for its toxic sap, which is used as a highly durable lacquer. The sap contains the allergenic compound urushiol, which gets its name from the Japanese name of the species, urushi. Unpigmented lacquer is dark brown, but the most common colors of urushiol finishes are black and red. Urushi lacquer is very stable. It withstands alkali, acid and alcohol and resists temperatures of over 300 °C, but UV rays from the sun and other sources can degrade it. The enzyme laccase takes its name from lacquer: it was first studied in the sap of the Japanese lacquer tree, where it helps to form lacquer.
Urushi chemistry
Urushiol makes up 60-65% of the sap and consists of catechol derivatives with a long alkyl side chain that carries unsaturated double bonds. The oxidation and polymerization of urushiol in the sap, in the presence of moisture, allows it to form a hard lacquer. Drying is demanding, since it requires approximately 70-90% relative humidity at 20-30 °C.
Shellac
Shellac is a resin secreted by the female lac bug on trees in the forests of India and Thailand. It is scraped from the bark of the trees where the lac bug, Kerria lacca, secretes it. Chemically, it is mainly composed of aleuritic acid, jalaric acid, shellolic acid and other natural waxes. It is sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish. Applied to a piece of wood, the dissolved shellac is an evaporative finish: the alcohol evaporates and leaves a protective film. Shellac is much softer than urushi lacquer, which is far superior in both chemical and mechanical resistance. Shellac was one of the dominant wood finishes in the western world until nitrocellulose lacquer largely replaced it in the 1920s and 1930s.
Decoration and other lacquers
After the lacquer is applied, decoration is added; the application of gold powder is known as maki-e. Raden uses inlays of shell and ivory to decorate pieces that usually have a wood base. Shunkei-nuri is made with transparent lacquer on yellow- or red-stained wood, so that the natural wood grain can be seen. In the Kamakura period, many Japanese craftsmen created Kamakurabori, a method of carving wood and then coating it with lacquer. Barniz de Pasto is a lacquer-like varnish technique that originated in the Pre-Columbian era and is a specialty of Pasto, Colombia; it is made by chewing the resin of the Andean mopa-mopa shrub.
