Linseed oil

{{short description|Oil obtained from the dried, ripened seeds of the flax plant}} {{use dmy dates|date=September 2025}} thumb|upright=1.35|Flax, flax seeds, linseed oil, linseed cake '''Linseed oil''', also known as '''flaxseed oil''' or '''flax oil''' (in its edible form), is a colorless 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 since the 1950s with increased availability of synthetic alkyd resins, which function similarly, are petroleum-based, and resist yellowing.<ref>{{cite book |last=Jones |first=Frank N. |year=2003 |chapter=Alkyd resins |title=Ullmann's Encyclopedia of Industrial Chemistry |isbn=978-3-5273-0673-2 |doi=10.1002/14356007.a01_409}}</ref>

==Structure and composition== :[[image:Triglyceride unsaturated Structural Formulae V2.svg|thumb|450px|right|Representative triglyceride found in a linseed oil, a triester (triglyceride) derived of '''linoleic acid''', '''alpha-linolenic acid''', and '''oleic acid''']] 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:<ref name=vereshagin>{{cite journal |last1=Vereshchagin |first1=A. G. |last2=Novitskaya |first2=Galina V. |year=1965 |title=The triglyceride composition of linseed oil |journal=Journal of the American Oil Chemists' Society |volume=42 |issue=11 |pages=970–974 |doi=10.1007/BF02632457 |pmid=5898097 |s2cid=29785363}}</ref> *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 properties== {{main|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 autoxidation, results in the rigidification of the material.<ref name=Poth-2001-UEIC>{{cite book |last=Poth |first=Ulrich |year=2001 |chapter=Drying oils and related products |title=Ullmann's Encyclopedia of Industrial Chemistry |doi=10.1002/14356007.a09_055 |isbn=9783527303854}}</ref> To prevent premature drying, linseed oil-based products (oil paints, putty) are stored in airtight containers.

Rags soaked with linseed oil pose a 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.<ref>{{cite journal |last1=Ettling |first1=Bruce V. |last2=Adams |first2=Mark F. |year=1971 |title=Spontaneous combustion of linseed oil in sawdust |journal=Fire Technology |volume=7 |issue=3 |pages=225 |doi=10.1007/BF02590415 |s2cid=109500727}}</ref> 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.<ref>{{cite report |first1=J. Gordon |last1=Routley |first2=Charles |last2=Jennings |first3=Mark |last3=Chubb |date=February 1991 |title=Highrise Office Building Fire, One Meridian Plaza, Philadelphia, Pennsylvania |series=United States Fire Administration |publisher=US DHS |id=report USFA-TR-049 |url=http://www.usfa.dhs.gov/downloads/pdf/publications/tr-049.pdf |via=usfa.dhs.gov |archive-date=24 February 2011 |access-date=19 August 2011 |archive-url=https://web.archive.org/web/20110224112440/http://www.usfa.dhs.gov/downloads/pdf/publications/tr-049.pdf |url-status=dead }}</ref>

==Applications== 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.<ref name=Poth-2001-UEIC/>

===Paint binder=== [[File:"YOUR COUNTRY NEEDS FLAX, AND WILL PAY WELL FOR IT." - NARA - 516250.jpg|thumb|"Your country needs flax..." U.S. WWII poster soliciting linseed oil for use in paint]] thumb|A can of French linseed oil

Linseed oil is the 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.{{citation needed|date=April 2022}}

===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 durability of putty is owed to the drying properties of linseed oil.{{citation needed|date=April 2022}}

===Wood finish=== When used as a wood finish, linseed oil dries slowly and shrinks little upon hardening. A linseed oil finish is easily scratched and liquid water penetrates a linseed oil finish in mere minutes, and water vapour bypasses it almost completely.<ref>{{cite book |last=Flexner |first=Bob |year=2005 |title=Understanding Wood Finishing |publisher=Reader's Digest Association |page=75}}</ref> Garden furniture treated with linseed oil may develop mildew. Oiled wood may be yellowish and is likely to darken with age. Even though the oil feels dry to the touch, studies show linseed oil does not fully cure.<ref>{{cite journal |last1=Lazzari |first1=Massimo |last2=Chiantore |first2=Oscar |year=1999 |title=Drying and oxidative degradation of linseed oil |journal=Polymer Degradation and Stability |volume=65 |issue=2 |pages=303–313 |doi=10.1016/S0141-3910(99)00020-8 |s2cid=96738494 |url=https://project-cms-rpc-endcap.web.cern.ch/rpc/Production/Oil%20&%20Bakelite/Oil/Documentation/1-s2.0-S0141391099000208-main%20Copy.pdf}}</ref>

Linseed oil is a common finish for wooden items, though very fine finish may require months to obtain. Studies show the fatty-acid structure of linseed oil has problems cross-linking and oxidizing, frequently turning black.<ref>{{cite journal |last1=Kerschner |first1=Richard L. |last2=Ravenel |first2=Nancie |year=2013 |title=Here we go 'round again: Cleaning linseed oil from carousel ''animalsatthe'' {{grey|[at the]}} Shelburne Museum |journal=Journal of the American Institute for Conservation |volume=45 |issue=3 |pages=201–210 |doi=10.1179/019713606806112450 |s2cid=191561961 |url=https://doi.org/10.1179/019713606806112450|url-access=subscription}}</ref>

===Gilding=== Boiled linseed oil is used as sizing in traditional oil gilding to adhere sheets of gold leaf to a substrate (parchment, canvas, Armenian bole, etc.). It has a much longer working time than water-based size and gives a firm smooth surface that is adhesive enough in the first 12–24 hours after application to cause the gold to attach firmly to the intended surface.{{citation needed|date=April 2022}}

===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 the 1970s, when it was largely replaced by PVC ("vinyl") floor coverings.<ref>S. Diller and J. Diller, ''Craftsman's Construction Installation Encyclopedia'', Craftsman Book Company, 2004, [https://books.google.com/books?id=vTVE7kRgQ38C&pg=PA503 p. 503]</ref> However, since the 1990s, linoleum is returning to favor, being considered more environmentally sound than PVC.<ref>Julie K. Rayfield, ''The Office Interior Design Guide: An Introduction for Facility and Design Professionals'', John Wiley & Sons, 1994, [https://books.google.com/books?id=uOliu8yjoTEC&pg=PA209 p. 209]</ref> 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.{{Citation needed|date=April 2022}}

===Nutritional supplement and food=== Raw cold-pressed linseed oil – commonly known as flax seed oil in nutritional contexts – is easily oxidized, and rapidly becomes rancid, with an unpleasant odour, unless refrigerated. Linseed oil is not generally recommended for use in cooking. In one study, the content of ''alpha''-linolenic acid (ALA) in whole flaxseeds did not decrease after heating the seeds to temperatures of up to 178 °C (352.4 °F) for one and a half hours.<ref>{{cite journal |title=Oxidative stability of flaxseed lipids during baking |journal=Journal of the American Oil Chemists' Society |volume=71 |issue=6 |pages=629–632 |doi=10.1007/BF02540591 |year = 1994|last1 = Chen|first1 = Z. Y.|last2=Ratnayake |first2=W. M. N. |last3=Cunnane |first3=S. C. |bibcode=1994JAOCS..71..629C |s2cid=84981982}}</ref>

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.{{citation needed|date=December 2024}}

Food-grade flaxseed oil is cold-pressed, obtained without solvent extraction, in the absence of oxygen, 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 nutty flavor. Regular flaxseed oil contains between 57% and 71% polyunsaturated fats (alpha-linolenic acid, linoleic acid). Plant breeders have developed flaxseed with both higher ALA (70%)<ref name=Morris-2007-FCC> {{cite web |first=Diane H. |last=Morris |year=2007 |title=Chapter 1: Description and composition of flax |department=Flax – a health and nutrition primer |series=Technical nutrition information |website=Flax Council of Canada (flaxcouncil.ca) |url=https://flaxcouncil.ca/resources/nutrition/technical-nutrition-information/flax-a-health-and-nutrition-primer/ |access-date=16 September 2019 |url-status=dead |archive-url=https://web.archive.org/web/20220615120914/https://flaxcouncil.ca/resources/nutrition/technical-nutrition-information/flax-a-health-and-nutrition-primer/ |archive-date=15 June 2022 }} </ref> and very low ALA content {{nobr|(< 3%).<ref> {{cite book | editor1-last=Thompson | editor1-first=Lilian U. | editor2-last=Cunnane | editor2-first=Stephen C. | year = 2003 | title = Flaxseed in Human Nutrition | edition = 2nd | publisher = AOCS Press | pages = 8–11 | isbn = 978-1-893997-38-7 }} </ref>}} The USFDA granted ''g''enerally ''r''ecognized ''a''s ''s''afe (GRAS) status for high-alpha linolenic flaxseed oil.<ref> {{cite web |title=GRAS Notice {{nobr|No. GRN 00256}} |department=U.S. FDA / CFSAN Agency Response Letter |series=Center for Food Safety and Applied Nutrition (CFSAN) |website=www.accessdata.fda.gov |publisher=U.S. Food and Drug Administration |url=http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=grasListing&id=256 |url-status=dead |access-date=2013-01-29 |archive-url=https://web.archive.org/web/20091011105715/http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=grasListing&id=256 |archive-date=11 October 2009 }} </ref>

==== Nutrient content ==== :{| class="wikitable" style="text-align:center;" |+ '''Nutrition information''' from IENICA<ref name=IENICA/> and DGFETT<ref name=DGF/> |- style="vertical-align:bottom;" ! Typical fatty acid content ! %<ref name=IENICA> {{cite web | title=Linseed | date=14 October 2002 | publisher=Interactive European Network for Industrial Crops and their Applications | website=ienica.net | url=http://www.ienica.net/crops/linseed.pdf | url-status=dead | access-date=2008-01-24 | archive-url=https://web.archive.org/web/20070927235105/http://www.ienica.net/crops/linseed.pdf | archive-date=September 27, 2007 }} </ref> (IENICA) ! %<ref name=DGF> {{cite web |title=Leinöl europa |lang=de |trans-title={{grey|European linseed oil}} |department=Fettsäurezusammensetzung wichtiger pflanzlicher und tierischer Speisefette und -öle {{grey|[Fatty acid composition of important plant and animal dietary fats and oils]}} |publisher=Deutsche Gesellschaft für Fettwissenschaft {{grey|[German Society for Lipid Research]}} |website=dgfett.de |url=http://www.dgfett.de/material/fszus.htm |archive-url=https://web.archive.org/web/20081222233514/http://www.dgfett.de/material/fszus.htm |archive-date=2008-12-22 }} </ref> (DGFETT) |- |align="left"| Palmitic acid | 6.0 | 4.0–6.0 |- |align="left"| Stearic acid | 2.5 | 2.0–3.0 |- |align="left"| Arachidic acid | 0.5 | 0–0.5 |- |align="left"| Palmitoleic acid | - | 0–0.5 |- |align="left"| Oleic acid | 19.0 | 10.0–22.0 |- |align="left"| Eicosenoic acid | - | 0–0.6 |- |align="left"| Linoleic acid | 24.1 | 12.0–18.0 |- |align="left"| Alpha-linolenic acid | 47.4 | 56.0–71.0 |- | Other | 0.5 | - |} :{| class="wikitable" |+ '''Nutrition information''' from the {{nobr|Flax Council of Canada}} |- |colspan=2 style="text-align:center;font-style:italic;"| {{nobr| Per 1 tbsp (14 g)<ref name=fcac> {{cite web |title=Flax – a healthy food |publisher=Flax Council of Canada |website=flaxcouncil.ca |url=http://www.flaxcouncil.ca/english/index.jsp?p=g1&mp=nutrition |lang=en |url-status=dead |access-date=2008-01-24 |archive-url=https://web.archive.org/web/20110706180422/http://www.flaxcouncil.ca/english/index.jsp?p=g1&mp=nutrition |archive-date=2011-07-06 }} </ref> }} |- | Calories ||align="right"| 126 k·cal |- | Omega-3 ||align="right"| 8 g |- | Omega-6 ||align="right"| 2 g |- | Omega-9 ||align="right"| 3 g |- | Total fat ||align="right"| 14 g |- |colspan=2 style="font-size:75%;" align="center"| Flax seed oil contains no significant amounts of protein, carbohydrates, or fibre. |}

===Comparison to other vegetable oils===

===Additional uses=== {{more citations needed|section|date=January 2021}} {{div col begin|colwidth=13em}} * Animal care products * Bicycle maintenance (as a thread fixative, rust inhibitor, and lubricant) * Composition ornament for moulded decoration * Earthen floors * Animal feeds * Industrial lubricant * Leather treatment * Oilcloth * Particle detectors<ref> {{cite conference |first=Leah |last=Goldberg |date=2008-10-26 |title=Measuring rate capability of a bakelite-trigger RPC coated with linseed oil |conference=APS Division of Nuclear Physics Meeting |series=Abstracts |volume=DA.033 |publisher=American Physical Society |bibcode=2008APS..DNP.DA033G }} </ref> * Textiles * Wood preservative (including as an active ingredient of Danish oil) * Cookware seasoning * Plant protection<ref> {{cite journal |last1=Breiing |first1=Vera |last2=Hillmer |first2=Jennifer |last3=Schmidt |first3=Christina |last4=Petry |first4=Michael |last5=Behrends |first5=Brigitte |last6=Steiner |first6=Ulrike |last7=Kraska |first7=Thorsten |last8=Pude |first8=Ralf |display-authors=6 |year=2021 |title=Fungicidal efficacy of drying plant oils in green beans against bean rust (''Uromyces appendiculatus'') |journal=Plants |volume=10 |issue=1 |page=143 |doi=10.3390/plants10010143 |doi-access=free |pmid=33445566 |pmc=7827098 |bibcode=2021Plnts..10..143B }} </ref> {{div col end}}

==Modified linseed oils==

===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 dienes, which then undergo Diels-Alder reactions, 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 can be treated similarly, but converts more slowly. On the other hand, tung oil 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.<ref name=Poth-2001-UEIC/>

===Boiled linseed oil=== Boiled linseed oil is a combination of raw linseed oil, stand oil (see above), and metallic oil drying agents (catalysts to accelerate drying).<ref name=Poth-2001-UEIC/> In the Medieval era, linseed oil was boiled with lead oxide (litharge) to give a product called ''boiled linseed oil'':<ref> {{cite book |last=Merrifield |first=Mary P. |year=2012 |title=Medieval and Renaissance Treatises on the Arts of Painting: Original texts |publisher=Dover Publications |isbn=978-0486142241 |pages={{math|''ccxxxviii–ccxli''}} |url=https://books.google.com/books?id=C-uiAK74XpsC&q=boiled+linseed+oil+litharge&pg=PR238 |via=Google }} </ref> The lead oxide forms lead "soaps" (lead oxide is alkaline) that promote hardening (polymerisation) of linseed oil by reaction with atmospheric oxygen. Heating shortens its drying time.{{citation needed|date=April 2022}}

=== Raw linseed oil === Raw linseed oil is the base oil, unprocessed and without driers or thinners. It is mostly used as a feedstock for making a boiled oil. It does not cure sufficiently well or quickly to be regarded as a drying oil.<ref> {{cite book |first=George |last=Franks |year=1999 |title=Classic Wood Finishing |edition=2nd |publisher=Sterling |isbn=978-0806970639 |page=96 }} </ref> Raw linseed is sometimes used for oiling cricket bats to increase surface friction for better ball control.<ref> {{cite web |title=Caring for your {{grey|[cricket]}} bat |website=Gunn & Moore (gm-cricket.com) |url=http://www.gm-cricket.com/pages/bat-care.aspx |url-status=dead |archive-url=https://web.archive.org/web/20170816010538/http://www.gm-cricket.com/pages/bat-care.aspx |archive-date=16 August 2017 }} </ref> It was also used to treat leather flat belt drives to reduce slipping.{{citation needed|date=April 2022}}

==References== {{reflist|25em}}

== Further reading == * {{cite web |first1=William A. |last1=Knight |first2=William R. |last2=Mende |year=2000 |title=Staining and finishing for muzzleloading gun builders |website=thealchemist.us |url=http://www.thealchemist.us/alchemist1_005.htm |archive-url=https://web.archive.org/web/20130530042026/http://www.thealchemist.us/alchemist1_005.htm |archive-date=2013-05-30 }}

==External links== {{Commons}} *{{Cite Collier's|wstitle=Linseed Oil |short=x}}

Category:Vegetable oils Category:Dietary supplements Category:Visual arts materials Category:Painting materials Category:Wood finishing materials Category:Oils Category:Flax

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