Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...

 plant (Linum usitatissimum, Linaceae
The Linaceae is a family of flowering plants. The family is cosmopolitan, and includes approximately 250 species. There are 14 genera, classified into two subfamilies: Linoideae and Hugonioideae ....

). The oil is obtained by cold pressing, sometimes followed by solvent extraction. Due to its high levels of α-Linolenic acid (a particular form of Omega-3 fatty acid
Omega-3 fatty acid
N−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....

), it is used as a nutritional supplement.

Linseed oil is a "drying oil
Drying oil
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen . Drying oils are a key component of oil paint and some varnishes...

", as it can polymerize
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 into a solid form.