Since the time of the Renaissance, siccative (drying) oil paints, primarily linseed oil, have been the most commonly used kind of paints in fine art applications; oil paint is still common today. However, in the 20th century, water-based paints, including watercolors and acrylic paints, became very popular with the development of acrylic and other latex paints. Milk paints (also called casein), where the medium is derived from the natural emulsion that is milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is an emulsion of raw egg yolk mixed with oil) is still in use as well, as are encaustic wax-based paints. Gouache is a variety of opaque watercolor which was also used in the Middle Ages and Renaissance for manuscript illuminations. The pigment was often made from ground semiprecious stones such as lapis lazuli and the binder made from either gum arabic or egg white. Gouache, also known as 'designer color' or 'body color' is commercially available today. Poster paint has been used primarily in the creation of student works, or by children. Linseed oil, also known as flaxseed oil, is a colorless to yellowish oil obtained from the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae). The oil is obtained by pressing, sometimes followed by solvent extraction. Due to its high levels of ?-Linolenic acid (a particular form of Omega-3 fatty acid), it is used as a nutritional supplement. Linseed oil is a "drying oil", as it can polymerize into a solid form. Due to its polymer-forming properties, linseed oil is used on its own or blended with

ther oils, resins, and solvents as an impregnator and varnish in wood finishing, as a pigment binder in oil paints, as a plasticizer and hardener in putty and in the manufacture of linoleum. The use of linseed oil has declined over the past several decades with the increased use of synthetic alkyd resins, which function similarly but resist yellowing.[1] Linseed oil is an edible oil marketed as a nutritional supplement. In parts of Europe, it is traditionally eaten with potatoes and quark (cheese). It is regarded as a delicacy due to its hearty taste, which spices the bland quark.[2] Linseed oil is a triglyceride, like other fats. Linseed oil is distinctive in terms of fatty acid constituents of the triglyceride, which contain an unusually large amount of ?-linolenic acid, which has a distinctive reaction toward oxygen in air. Specifically, the constituent fatty acids in a typical linseed oil are of the following types:[3] The triply unsaturated ?-linolenic acid (51.9-55.2%), The saturated acids palmitic acid (about 7%) and stearic acid (3.4-4.6%), The monounsaturated oleic acid (18.5-22.6%), The doubly unsaturated linoleic acid (14.2-17%). Having a high content of di- and triunsaturated esters, linseed oil is particularly susceptible to polymerization reactions upon exposure to oxygen in air. This polymerization, which is called "drying," results in the rigidification of the material. The drying process can be so exothermic as to pose a fire hazard under certain circumstances. To prevent premature drying, linseed oil-based products (oil paints, putty) should be stored in air-tight containers.