Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (Linum usitatissimum). The oil is obtained by pressing, sometimes followed by solvent extraction.
Owing to its polymer-forming properties, linseed oil is often blended with combinations of other oils, resins or solvents as an impregnator, drying oil finish or varnish in wood finishing, as a pigment binder in oil paints, as a plasticizer and hardener in putty, and in the manufacture of linoleum. Linseed oil use has declined over the past several decades with increased availability of synthetic alkyd resins—which function similarly but resist yellowing.
Linseed oil is an edible oil in demand as a dietary supplement, as a source of α-Linolenic acid, an omega-3 fatty acid. In parts of Europe, it is traditionally eaten with potatoes and quark.
Linseed oil is a triglyceride, like other fats. Linseed oil is distinctive for its unusually large amount of α-linolenic acid, which oxidises in air. The fatty acids in a typical linseed oil are of the following types:
The triply unsaturated α-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%).
drying oil
Having a high content of di- and tri-unsaturated esters, linseed oil is susceptible to polymerization reactions upon exposure to oxygen in air. This polymerization, which is called "drying", results in the rigidification of the material. To prevent premature drying, linseed oil-based products (oil paints, putty) are stored in airtight containers.
Rags soaked with linseed oil stored pose fire hazard because they provide a large surface area for rapid oxidation. The oxidation of linseed oil is exothermic, which may lead to spontaneous combustion. In 1991, One Meridian Plaza, in Philadelphia, was severely damaged in a fire, in which three firefighters perished, thought to be caused by rags soaked with linseed oil.