linseed oil

linseed oil

linseed oil, amber-colored, fatty oil extracted from the cotyledons and inner coats of the linseed. The raw oil extracted from the seeds by hydraulic pressure is pale in color and practically without taste or odor. When boiled or extracted by application of heat and pressure, it is darker and has a bitter taste and an unpleasant odor. Linseed oil has long been used as a drying oil in paints and varnish. It is also used in making linoleum, oilcloth, and certain inks.

Linseed oil, also known as flax seed oil or simply flax oil, is a clear to yellowish drying oil derived from the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae). It is obtained by pressing, followed by an optional stage of solvent extraction. Cold-pressed oil obtained without solvent extraction is marketed as flaxseed oil.

Uses

Paint binder

Linseed oil is the most commonly used carrier 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).

Putty

Glazing putty, consisting of a paste of chalk powder and linseed oil, is a traditional sealant for glass windows that dries hard within a few weeks and can then be painted over.

Wood finish

When used as a wood finish, 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. Wood treated with linseed oil is resistant to denting and scratches are easily repaired, but the wood and oil surface is not as hard as a modern varnish, and it slowly absorbs moisture if allowed to stay wet. Soft wood benefits from the protection from denting but requires more applications and even more drying time than harder wood does, if the grain is to be completely filled. The oil penetrates deeply and fills the grain, because it dries slowly and shrinks little or not at all on hardening. Like other oil finishes Garden furniture treated with linseed oil may develop mildew. Linseed oil is not completely denatured, so it can encourage rather than discourage mildew growth. Oiled wood is yellowish and darkens with age.

It is a traditional finish for gun stocks, but 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, and thus has a special cultural place in cricket-playing countries.

Fire departments treat the wood handles of hand tools that have metal implements (axes, plaster hooks etc.) on them with Linseed oil as it does not create static electricity, unlike synthetic wood finishes like varnishes.

Linseed oil is often used by billiards/pool cue-makers for the shaft portion of the cue.

Linseed oil is also commonly used as a lubricant/protectant for wooden recorders.

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 high levels of omega-3 fatty acids, especially alpha-linolenic acid, which has been suggested to 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 flax seed oil may not reduce the risk of stroke, heart disease, or cancer any greater than placebo. Regular flaxseed oil contains between 52 and 63 % alpha linolenic acid (C18:3 n-3). Plant breeders have developed flaxseed with high alpha linoleic acid content (70 %) and very low alpha linolenic acid content (< 3%).

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. In fact, flax seed oil is easily oxidized, and rapidly becomes rancid with an unpleasant odor unless refrigerated. Even when kept under cool conditions it has a shelf life of only a few weeks. Oil with an unpleasant or rancid odour should be discarded. Rancid oils contribute to the formation of free radicals and may be carcinogenic. Oxidation of flax seed oil is major commercial concern, and antioxidants may be added to prevent rancidification.

Nutrient content

Typical Fatty Acid Content %
Palmitic acid 6.0
Stearic acid 2.5
Arachidic acid 0.5
Oleic acid 19.0
Linoleic acid 24.1
Linolenic acid 47.4
Other 0.5

Nutrition information from the Flax Council of Canada.

Per 1 Tbsp (14 g)

Flax seed oil contains no significant amounts of protein, carbohydrates, or fibre.

Additional uses

Boiled linseed oil

Boiled linseed oil is used as a paint binder or as a wood finish on its own. Heating the oil makes it polymerize and oxidize, effectively making it thicker and shortening the drying time. Today most products labeled as "boiled linseed oil" are a combination of raw linseed oil, petroleum-based solvent and metallic dryers. The use of metallic dryers makes boiled linseed oil inedible. There are some products available that contain only heat-treated linseed oil, without exposure to oxygen. Heat treated linseed oil is thicker and dries very slowly. These are usually labeled as "polymerized" or "stand" oils, though some may still be labeled as boiled.

Spontaneous combustion

Rags dampened with boiled linseed oil are considered a fire hazard because they provide a large surface area for oxidation of the oil. The oxidation of linseed oil is an exothermic reaction which accelerates as the temperature of the rags increases. If rate of heat accumulation exceeds the rate of dissipation, this reaction may eventually become sufficiently hot to cause spontaneous combustion of the rags. Linseed oil soaked rags should never be stored in an enclosed container. Instead rags should be washed, soaked with water, or incinerated. A fire that destroyed the El Rey Theater-Golden West Saloon in February 2008 was ignited by the spontaneous combustion of linseed oil soaked rags left in a plastic container.

See also

References

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