Linseed oil

Linseed oil

Overview
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax
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
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
Polymerization
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.
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Encyclopedia
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax
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
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
Polymerization
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. Due to its polymer-forming properties, linseed oil is used on its own or blended with other oils, resins, and solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s as an impregnator and varnish
Varnish
Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...

 in wood finishing
Wood finishing
Wood finishing refers to the process of embellishing and/or protecting the surface of a wooden material. The process starts with surface preparation, either by sanding by hand , scraping, or planing. Imperfections or nail holes on the surface may be filled using wood putty or pores may be filled...

, as a pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 binder in oil paint
Oil paint
Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...

s, as a plasticizer
Plasticizer
Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...

 and hardener in putty
Putty
Putty is a generic term for a plastic material similar in texture to clay or dough typically used in domestic construction and repair as a sealant or filler. Painter's Putty is typically a linseed oil based product used for filling holes, minor cracks and defacements in wood only...

 and in the manufacture of linoleum
Linoleum
Linoleum is a floor covering made from renewable materials such as solidified linseed oil , pine rosin, ground cork dust, wood flour, and mineral fillers such as calcium carbonate, most commonly on a burlap or canvas backing; pigments are often added to the materials.The finest linoleum floors,...

. The use of linseed oil has declined over the past several decades with the increased use of synthetic alkyd
Alkyd
An alkyd is a polyester modified by the addition of fatty acids and other components. They are derived from polyols and a dicarboxylic acid or carboxylic acid anhydride. The term alkyd is a modification of the original name "alcid", reflecting the fact that they are derived from alcohol and...

 resins, which are functionally similar but resist yellowing. It is an edible oil but, because of its strong flavor and odor, is only a minor constituent of human nutrition in the U.S., although it is marketed as a nutritional supplement. In parts of Europe, it is traditionally eaten with potatoes and quark (cheese)
Quark (cheese)
Quark is a type of fresh cheese, also known as tvorog , topfen , biezpiens , and varškė . It is made by warming soured milk until the desired degree of denaturation of milk proteins is met, and then strained...

. It is regarded as a delicacy due to its hearty taste, which spices the bland quark.

Chemical aspects


Linseed oil is a triglyceride
Triglyceride
A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....

, like other fats. Linseed oil is distinctive in terms of fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 constituents of the triglyceride, which contain an unusually large amount of α-linolenic acid
Alpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....

, which has a distinctive reaction toward oxygen in air. Specifically, the constituent 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
    Palmitic acid
    Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...

     (about 7%) and stearic acid
    Stearic acid
    Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

     (3.4-4.6%),
  • The monounsaturated oleic acid
    Oleic acid
    Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...

     (18.5-22.6%),
  • The doubly unsaturated linoleic acid
    Linoleic acid
    Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...

     (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.

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
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

-based material is advantageous.

Paint binder


Linseed oil is a common carrier used in oil paint
Oil paint
Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...

. 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
Putty
Putty is a generic term for a plastic material similar in texture to clay or dough typically used in domestic construction and repair as a sealant or filler. Painter's Putty is typically a linseed oil based product used for filling holes, minor cracks and defacements in wood only...

, consisting of a paste of chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....

 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
Wood finishing
Wood finishing refers to the process of embellishing and/or protecting the surface of a wooden material. The process starts with surface preparation, either by sanding by hand , scraping, or planing. Imperfections or nail holes on the surface may be filled using wood putty or pores may be filled...

, 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. A linseed oil finish is easily repaired, but it provides no significant barrier against scratching. Only wax finishes are less protective. Liquid water will penetrate a linseed oil finish in mere minutes and water vapour bypasses it almost completely. Garden furniture
Garden furniture
Garden furniture, also called patio furniture and outdoor furniture, is a type of furniture specifically designed for outdoor use. It is typically made of weather resistant materials...

 treated with linseed oil may develop mildew
Mildew
Mildew refers to certain kinds of molds or fungi.In Old English, it meant honeydew , and later came to mean mildew in the modern sense of mold or fungus....

. Oiled wood may be yellowish and is likely to darken with age. Because it fills the pores, linseed oil protects wood from denting by compression.

Linseed oil is a traditional finish for gun stocks, although very fine finish may require months to obtain. Several coats of linseed oil is the traditional protective coating for the raw willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

 wood of cricket
Cricket
Cricket is a bat-and-ball game played between two teams of 11 players on an oval-shaped field, at the centre of which is a rectangular 22-yard long pitch. One team bats, trying to score as many runs as possible while the other team bowls and fields, trying to dismiss the batsmen and thus limit the...

 bats. Linseed oil is also often used by billiards
Billiards
Cue sports , also known as billiard sports, are a wide variety of games of skill generally played with a cue stick which is used to strike billiard balls, moving them around a cloth-covered billiards table bounded by rubber .Historically, the umbrella term was billiards...

 or pool
Pocket billiards
Pool, also more formally known as pocket billiards or pool billiards , is the family of cue sports and games played on a pool table having six receptacles called pockets along the , into which balls are deposited as the main goal of play. Popular versions include eight-ball and nine-ball...

 cue-makers for cue shafts
Cue stick
A cue stick , is an item of sporting equipment essential to the games of pool, snooker and carom billiards. It is used to strike a ball, usually the...

, as a lubricant/protectant for wooden recorders, and used in place of epoxy to seal modern wooden surfboard
Surfboard
A surfboard is an elongated platform used in the sport of surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding a breaking wave...

s. It is used to coat cricket bats so that the wood will retain some moisture. New cricket bats are coated with linseed oil and knocked to perfection so they last longer.

Additionally, a luthier
Luthier
A luthier is someone who makes or repairs lutes and other string instruments. In the United States, the term is used interchangeably with a term for the specialty of each maker, such as violinmaker, guitar maker, lute maker, etc...

 may use linseed oil when reconditioning a guitar
Guitar
The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...

, mandolin
Mandolin
A mandolin is a musical instrument in the lute family . It descends from the mandore, a soprano member of the lute family. The mandolin soundboard comes in many shapes—but generally round or teardrop-shaped, sometimes with scrolls or other projections. A mandolin may have f-holes, or a single...

, or other stringed instrument's fret board; lemon
Lemon
The lemon is both a small evergreen tree native to Asia, and the tree's ellipsoidal yellow fruit. The fruit is used for culinary and non-culinary purposes throughout the world – primarily for its juice, though the pulp and rind are also used, mainly in cooking and baking...

-scented mineral oil
Mineral oil
A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....

 is commonly used for cleaning, then a light amount of linseed oil (or other drying oil) is applied to protect it from grime that might otherwise result in accelerated deterioration of the wood.

Linoleum


Linseed oil is used to bind wood dust, cork particles, and related materials in the manufacture of the floor covering linoleum
Linoleum
Linoleum is a floor covering made from renewable materials such as solidified linseed oil , pine rosin, ground cork dust, wood flour, and mineral fillers such as calcium carbonate, most commonly on a burlap or canvas backing; pigments are often added to the materials.The finest linoleum floors,...

. After its invention in 1860 by Frederick Walton
Frederick Walton
Frederick Edward Walton , was an English manufacturer and inventor who invented Linoleum in Staines and Lincrusta ....

, linoleum, or "lino" for short, was a common form of domestic and industrial floor covering from the 1870s until its virtual replacement by PVC
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...

 floor coverings. Linoleum has given its name to the printmaking technique linocut
Linocut
Linocut is a printmaking technique, a variant of woodcut in which a sheet of linoleum is used for the relief surface. A design is cut into the linoleum surface with a sharp knife, V-shaped chisel or gouge, with the raised areas representing a reversal of the parts to show printed...

, 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
Woodcut
Woodcut—occasionally known as xylography—is a relief printing artistic technique in printmaking in which an image is carved into the surface of a block of wood, with the printing parts remaining level with the surface while the non-printing parts are removed, typically with gouges...

 printing.

Nutritional supplement and food


Although flax seeds contain lignan
Lignan
The lignans are a group of chemical compounds found in plants. Lignans are one of the major classes of phytoestrogens, which are estrogen-like chemicals and also act as antioxidants. The other classes of phytoestrogens are the isoflavones and coumestans...

s, 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 odor
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...

, unless refrigerated
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

. 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
Rancidification
Rancidification is the chemical decomposition of fats, oils and other lipids . When these processes occur in food, undesirable odors and flavors can result. In some cases, however, the flavors can be desirable . In processed meats, these flavors are collectively known as "warmed over flavor"...

. The alpha linolenic acid (ALA) in flaxseed oil is suitable for cooking, as it (and the lignans in flax seeds themselves) can withstand temperatures up to 350 degrees F for two hours.

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 and is a traditional European ethnic food, highly regarded for its hearty taste. It contains the highest level of the 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....

 ALA among vegetable oils. Regular flaxseed oil contains between 52% and 63% ALA (C18:3 n-3). Plant breeders have developed flaxseed with both higher ALA (70%) and very low ALA content (< 3%). The USFDA granted generally recognized as safe (GRAS) status for high alpha linolenic flaxseed oil.

According to the Flax Council of Canada, ALA is required for normal infant development and may be beneficial for reducing inflammation leading to atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...

, and for preventing heart disease and arrhythmia. However, recent well-controlled placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

 studies suggest the regular consumption of flaxseed oil may not reduce the risk of stroke, heart disease, or cancer.

Studies have shown a relationship between ALA and an increased risk of prostate cancer. This risk was found to be irrespective of source (e.g., meat, vegetable oil). Alternatively, at least one meta analysis has found a weak protective association between dietary ALA intake and prostate cancer risk.

Nutrient content

Typical fatty acid content % % European
Palmitic acid
Palmitic acid
Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...

6.0 4.0–6.0
Stearic acid
Stearic acid
Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

2.5 2.0–3.0
Arachidic acid
Arachidic acid
Arachidic acid, also called eicosanoic acid, is the saturated fatty acid with a 20 carbon chain. It is as a minor constituent of peanut oil and corn oil . Its name derives from the Latin arachis — peanut...

0.5 0–0.5
Palmitoleic acid
Palmitoleic acid
Palmitoleic acid, or -9-hexadecenoic acid, is an omega-7 monounsaturated fatty acid with the formula CH35CH=CH7COOH that is a common constituent of the glycerides of human adipose tissue. It is present in all tissues, but generally found in higher concentrations in the liver...

- 0–0.5
Oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...

19.0 10.0–22.0
Eicosenoic acid
Eicosenoic acid
Eicosenoic acid is a monounsaturated omega-9 fatty acid found in a variety of plant oils....

- 0–0.6
Linoleic acid
Linoleic acid
Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...

24.1 12.0–18.0
Alpha-linolenic acid
Alpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....

47.4 56.0–71.0
Other 0.5 -


Nutrition information from the Flax Council of Canada.

Per 1 Tbsp (14 g)
  • Calories: 124
  • Total fat
    Fatty acid
    In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

    : 14g
  • Omega-3: 8g
  • Omega-6: 2g
  • Omega-9: 3g


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

Additional uses

  • Animal feeds
    Fodder
    Fodder or animal feed is any agricultural foodstuff used specifically to feed domesticated livestock such as cattle, goats, sheep, horses, chickens and pigs. Most animal feed is from plants but some is of animal origin...

  • Earthen floor
    Earthen floor
    An earthen floor, also called an adobe floor, is a floor made of dirt, raw earth, or other unworked ground materials. It is usually constructed, in modern times, with a mixture of sand, finely chopped straw and clay, mixed to a thickened consistency and spread with a trowel on a sub-surface such...

    s
  • Textile
    Textile
    A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

    s
  • Bicycle
    Bicycle
    A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

     maintenance as a thread fixative, rust inhibitor and lubricant
  • Leather
    Leather
    Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

     treatment
  • Composition ornament
    Composition ornament
    'Compo' is a mouldable resin worked either by hand or more usually pressed into moulds to produce decorative work. It's now most commonly seen as part of gilded picture frames, but was in use for many smaller decorative mouldings from the later part of the Baroque period. - A Compo recipe :A basic...

     for moulded decoration
  • Animal care products
  • Industrial lubricant
  • Particle Detector
    Particle detector
    In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...

    s
  • Oilcloth

Stand oil


Stand oil is generated by heating linseed oil near 300 °C for a few days in the complete absence of air. Under these conditions, the polyunsaturated fatty esters convert to conjugated diene
Diene
In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...

s, which then undergo Diels-Alder reaction
Diels-Alder reaction
The Diels–Alder reaction is an organic chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. The reaction can proceed even if some of the atoms in the newly formed ring are not carbon...

s, leading to crosslinking. The product, which is highly viscous, gives highly uniform coatings that "dry" to more elastic coatings than linseed oil itself. Soybean oil
Soybean oil
Soybean oil is a vegetable oil extracted from the seeds of the soybean . It is one of the most widely consumed cooking oils. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints...

 can be treated similarly, but converts more slowly. On the other hand, tung oil
Tung oil
Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree . As a drying oil, tung oil hardens upon exposure to air. The resulting coating is transparent plastic-like and is exploited in most of its applications, which include wood finishing and the...

 converts very quickly, being complete in minutes at 260 °C. Coatings prepared from stand oils are less prone to yellowing than are coatings derived from the parent oils.

Boiled linseed oil


Boiled linseed oil is used as a paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

 binder or as a wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

 finish on its own. Heating the oil causes it to polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

ize and oxidize, making it thicker and shortening its drying time. Today, most products labeled as "boiled linseed oil" are a combination of raw linseed oil, petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

-based solvent, and metallic dryers (catalysts to accelerate drying). The use of metallic dryers makes boiled linseed oil inedible. Some products contain only heat-treated linseed oil, without exposure to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. Heat-treated linseed oil is thicker and dries very slowly. This grade of linseed oil is usually labeled as "polymerized" or "stand" oil, though some types may still be labeled as "boiled".

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
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

 reaction, which accelerates
Thermal runaway
Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...

 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
One Meridian Plaza
One Meridian Plaza was a 38-story high-rise office building in Philadelphia, Pennsylvania, United States. The tower was designed by Vincent Kling & Associates and completed in 1972. The building was demolished in 1999 as a result of damage of a fire that began on February 23, 1991...

, a high rise in Philadelphia was severely damaged and three firefighters perished in a fire caused by linseed oil-soaked rags.
An apartment in Sacramento
Sacramento
Sacramento is the capital of the state of California, in the United States of America.Sacramento may also refer to:- United States :*Sacramento County, California*Sacramento, Kentucky*Sacramento – San Joaquin River Delta...

also caught fire due to the spontaneous combustion of linseed oil-soaked rags.