View source for Linseed oil

{{short description|Oil obtained from the dried, ripened seeds of the flax plant}}
{{use dmy dates|date=September 2025}}
[[File:From flax to linseed oil..JPG|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 [[Expeller pressing|pressing]], sometimes followed by solvent extraction.

Owing to its polymer-forming properties, linseed oil is often blended with combinations of other oils, [[resins]], or [[solvent]]s as an impregnator, drying oil finish, or [[varnish]] in [[wood finishing]]; as a [[pigment]] binder in [[oil paint]]s; 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|<span style="color:green;">'''linoleic acid'''</span>]], [[alpha-linolenic acid|<span style="color:red;">'''alpha-linolenic acid'''</span>]], and [[oleic acid|<span style="color:blue;">'''oleic acid'''</span>]]]]
Linseed oil is a [[triglyceride]], like other fats. Linseed oil is distinctive for its unusually large amount of [[alpha-linolenic acid|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 [[ester]]s, 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=[[United States Department of Homeland Security|US DHS]] |id=report&nbsp;USFA-TR-049 |url=http://www.usfa.dhs.gov/downloads/pdf/publications/tr-049.pdf |via=usfa.dhs.gov}}</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. [[World War II|WWII]] poster soliciting linseed oil for use in paint]]
[[File:Fransk Linolja - 2021.jpg|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 finishing|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 [[polyvinyl chloride|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 &ndash; commonly known as flax seed oil in nutritional contexts &ndash; is easily oxidized, and rapidly becomes rancid, with an unpleasant [[odour]], unless [[refrigeration|refrigerated]]. Linseed oil is not generally recommended for use in cooking. In one study, the content of [[alpha-linolenic acid|''alpha''-linolenic acid (ALA)]] in whole flaxseeds did not decrease after heating the seeds to temperatures of up to 178&nbsp;°C (352.4&nbsp;°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. |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 (dairy product)|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&nbsp;1: Description and composition of flax
 |department=Flax – a health and nutrition primer
 |series=Technical nutrition information
 |url=https://flaxcouncil.ca/resources/nutrition/technical-nutrition-information/flax-a-health-and-nutrition-primer/
 |website=Flax Council of Canada (flaxcouncil.ca)
 |access-date=16 September 2019
}}
</ref> and very low ALA content (< 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 <u>g</u>enerally <u>r</u>ecognized <u>a</u>s <u>s</u>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=[[Food and Drug Administration (United States)|U.S. Food and Drug Administration]] (accessdata.fda.gov)
 |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;"
|-
! Typical fatty acid content
! % (IENICA)<ref>
{{cite web
 | title=Linseed
 | date=October 14, 2002
 | website=Interactive European Network for Industrial Crops and their Applications (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>
! % (DGFETT)<ref name=DGF>
{{cite web
 |title=Leinöl europa |language=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]}}
 |website=Deutsche Gesellschaft für Fettwissenschaft (dgfett.de) {{grey|[German Society for Lipid Research]}}
 |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>
|-
|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
| -
|}

:{|
|+ {{nobr|Nutrition information from the}} Flax Council of Canada.<ref name=fcac>{{cite web
 |title=Flax - a healthy food
 |website=Flax Council of Canada (flaxcouncil.ca)
 |url=http://www.flaxcouncil.ca/english/index.jsp?p=g1&mp=nutrition
 |url-status=dead |language=en |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>
|-
|colspan=2 style="text-align:center;font-style:italic;"| {{nobr| &emsp; Per 1&nbsp;tbsp (14&nbsp;g) &emsp;}}
|-
| |[[Omega-3]] || {{right|8&nbsp;g}}
|-
| [[Omega-6]]  || {{right|2&nbsp;g}}
|-
| [[Omega-9]]  || {{right|3&nbsp;g}}
|-
| Total [[fatty acid|fat]] &emsp; || {{right|14&nbsp;g}}
|-
| [[food energy|Calories]] || {{right|126&nbsp;k·cal}}
|-
|colspan=2 style="font-size:75%;"|Flax seed oil contains no<br />significant amounts of protein,<br />carbohydrates, or fibre.
|}

===Comparison to other vegetable oils===
:{|
|-
| {{Vegetable_oils,_composition}}
|}

===Additional uses===
{{more citations needed|section|date=January 2021}}
{{div col begin|colwidth=13em}}
* Animal care products
* [[Bicycle]] maintenance<br />(as a thread fixative, rust inhibitor, and lubricant)
* [[Composition ornament]] for moulded decoration
* [[Earthen floor]]s
* [[Fodder|Animal feeds]]
* Industrial [[lubricant]]
* [[Leather]] treatment
* [[Oilcloth]]
* [[Particle detector]]s<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>
* [[Textile]]s
* [[Wood preservation#Linseed oil|Wood preservative]]<br />(including as an active ingredient of [[Danish oil]])
* [[Seasoning (cookware)|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 (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&nbsp;°C for a few days in the complete absence of air. Under these conditions, the polyunsaturated fatty esters convert to conjugated [[diene]]s, which then undergo [[Diels-Alder reaction]]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]] can be treated similarly, but converts more slowly. On the other hand, [[tung oil]] converts very quickly, being complete in minutes at 260&nbsp;°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 agent]]s (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 [[Cricket bat#Oiling|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 [[Belt (mechanical)#Flat belts|leather flat belt drive]]s to reduce slipping.{{citation needed|date=April 2022}}

==See also==
* [[Danish oil]]
* [[Flax#Flax seeds|Flax seed]]
* [[National Linseed Oil Trust]]
* [[Smoke point]]

==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}}

{{Dietary supplement}}
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{{Authority control}}

[[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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