Linseed oil
Linseed oil (also known as flax seed oil) is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae). The oil is obtained by cold pressing, sometimes followed by solvent extraction.
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 other 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 are functionally similar that resist yellowing. It is an edible oil but, because of its strong flavor and odor, is only a minor constituent of human nutrition, although it is marketed as a nutritional supplement.
Uses
Most applications of linseed oil exploit its drying properties, i.e. the initial material is liquid or at least pliable and the aged material is rigid but not brittle. The water-repelling (hydrophobic) nature of the resulting hydrocarbon-based material is advantageous.
Paint binder
Linseed oil is a common carrier used in oil paint. It can also be used as a painting medium, making oil paints more fluid, transparent and glossy. It is available in varieties such as cold pressed, alkali refined, sun bleached, sun thickened, and polymerised (stand oil). The introduction of linseed oil was a significant advance in the technology of oil painting.
Putty
Traditional glazing putty, consisting of a paste of chalk powder and linseed oil, is a sealant for glass windows that hardens within a few weeks of application and can then be painted over. The utility of putty is owed to the drying properties of linseed oil.
Wood finish
When used as a wood finish, linseed oil dries slowly and shrinks little upon hardening. Linseed oil does not cover the surface as varnish does, but soaks into the (visible and microscopic) pores, leaving a shiny but not glossy surface that shows off the grain of the wood. Wood treated with linseed oil is resistant to denting and scratches and is easily repaired, but the surface is not as hard as a modern varnish, and the wood will slowly absorb moisture if allowed to stay wet. Soft wood is protected from denting, but requires numerous applications and even more drying time than harder wood. Garden furniture treated with linseed oil may develop mildew. Oiled wood can be yellowish and can darken with age.
Linseed oil is a traditional finish for gun stocks. A very fine finish may require months to obtain. Several coats of linseed oil is the traditional protective coating for the raw willow wood of cricket bats. Linseed oil is also often used by billiards or pool cue-makers cue shafts, as a lubricant/protectant for wooden recorders, and used in place of epoxy to seal modern wooden surfboards.
Additionally, a luthier may use linseed oil when reconditioning a guitar, mandolin, or other stringed instrument's fret board; lemon oil is commonly used for this purpose. It is desirable, after cleaning a fret board, to apply a light amount of linseed oil to seal and protect it from moisture, skin oils, etc. that might otherwise result in accelerated deterioration of the wood. Also, it does not "expand" the wood when it soaks into the pores.
Linoleum
Linseed oil is used to bind wood dust, cork particles, and related materials in the manufacture of the floor covering linoleum. After its invention in 1860 by Frederick Walton, linoleum, or "lino" for short, was a common form of domestic and industrial floor covering from the 1870s until its virtual replacement by PVC floor coverings. Linoleum has given its name to the printmaking technique linocut, in which a relief design is cut into the smooth surface and then inked and used to print an image. The results are similar to those obtained by woodcut printing.
Nutritional supplement
Food-grade flaxseed oil is cold-pressed, obtained without solvent extraction, and marketed as edible flaxseed oil. Fresh, refrigerated and unprocessed, linseed oil is used as a nutritional supplement. It contains the highest level of omega-3 fatty acids among vegetable oils, especially alpha-linolenic acid, which may be beneficial for reducing inflammation leading to atherosclerosis, preventing heart disease and arrhythmia, and is required for normal infant development. However, recent well-controlled placebo studies suggest that regular consumption of flaxseed oil may not reduce the risk of stroke, heart disease, or cancer (however, the dosage is not stated). Regular flaxseed oil contains between 52 and 63% alpha linolenic acid (C18:3 n-3). Plant breeders have developed flaxseed with higher alpha linoleic acid content (70%) and very low alpha linolenic acid content (< 3%). The USFDA granted GRAS (Generally Recognized As Safe) status for high alpha linolenic flaxseed oil.
Although flax seeds themselves contain lignans, a class of phytoestrogens considered to have antioxidant and cancer-preventing properties, the extracted linseed oil does not contain the lignans found in flax seed, and therefore does not have the same antioxidant properties. Some brands of supplement have lignans added during production. Flax seed oil is easily oxidized, and rapidly becomes rancid with an unpleasant odour unless refrigerated. Even when kept under cool conditions it has a shelf life of only a few weeks. Oil with an unpleasant or rancid odor should be discarded. Oxidation of flax seed oil is major commercial concern, and antioxidants may be added to prevent rancidification.
Spontaneous combustion
Rags soaked with linseed oil stored in a pile are considered a fire hazard because they provide a large surface area for oxidation of the oil, and the oil oxidizes quickly. The oxidation of linseed oil is an exothermic reaction, which accelerates (Thermal runaway) as the temperature of the rags increases. When heat accumulation exceeds the rate of heat dissipation into the environment, the temperature increases and may eventually become hot enough to make the rags spontaneously combust. In 1991, One Meridian Plaza, a high rise in Philadelphia, was severely damaged and three firefighters perished in a fire caused by linseed oil-soaked rags.
- More information is available at [ Wikipedia:Linseed_oil ]
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