From the oriental lacquer tree Toxicodendron vernicifluum, a sap (emulsion) is obtained the oil-soluble components (urushiol) of which consist of a mixture of 3-n-pentadecylcatechols and very small amounts of 3-n-heptadecylcatechols. Urushiol is the basis of oriental lacquer. The sap is conditioned by removal of most of the water by specific techniques, and the clear liquid is called oriental lacquer. It is used in the Orient for coatings to produce exquisite art objects. Poison ivy also has as its active ingredients 3-n-pentadecylcatechols, but they have a high diene content, which does not cure effectively. In humans 3-n-alkylcatechols cause severe contact dermatitis. The components of drying oils are glycerin esters of fatty acids derived from the families of palmitic (hexadecanoic) and stearic (octadecanoic) acids. In the case of the urushiols, as well as of the glycerides of drying oils, high unsaturation (60%) in the form of trienes in the long aliphatic chains is essential for curing.