Editing Linseed oil

{{short description|Oil obtained from the dried, ripened seeds of the flax plant}}
[[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 over the past several decades with increased availability of synthetic [[alkyd]] resins—which function similarly but resist yellowing.<ref>{{cite book |doi=10.1002/14356007.a01_409 |chapter=Alkyd Resins |year=2003 |last1=Jones |first1=Frank N.|title=Ullmann's Encyclopedia of Industrial Chemistry |isbn=978-3527306732 }}</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 |doi=10.1007/BF02632457 |pmid=5898097 |title=The triglyceride composition of linseed oil |year=1965 |last1=Vereshchagin |first1=A. G. |last2=Novitskaya |first2=Galina V. |journal=Journal of the American Oil Chemists' Society |volume=42 |issue=11 |pages=970–974 |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=Ullmann>{{cite book |doi=10.1002/14356007.a09_055 |chapter=Drying Oils and Related Products |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2001 |last1=Poth |first1=Ulrich |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 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 |doi=10.1007/BF02590415 |title=Spontaneous combustion of linseed oil in sawdust |year=1971 |last1=Ettling |first1=Bruce V. |last2=Adams |first2=Mark F. |journal=Fire Technology |volume=7 |issue=3 |pages=225|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>{{citation|url=http://www.usfa.dhs.gov/downloads/pdf/publications/tr-049.pdf|title=Highrise Office Building Fire One Meridian Plaza Philadelphia, Pennsylvania|publisher=Federal Emergency Management Agency|first1=J. Gordon|last1=Routley|first2=Charles|last2=Jennings|first3=Mark|last3=Chubb|date=February 1991|work=Report USFA-TR-049}}</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=Ullmann/>

===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]]
[[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>Flexner, Bob. ''Understanding Wood Finishing''. Reader's Digest Association, Inc., 2005, p. 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 |title=Drying and oxidative degradation of linseed oil |journal=Polymer Degradation and Stability |date=1999 |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 |title=Here We Go 'Round Again: Cleaning Linseed Oil from Carousel Animalsatthe Shelburne Museum |journal=Journal of the American Institute for Conservation |date=2013 |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]]).<ref name="fcc">{{cite web |first1=Diane H. |last1=Morris |title=Chapter 1: Description and Composition of Flax; In: Flax – A Health and Nutrition Primer |url=https://flaxcouncil.ca/resources/nutrition/technical-nutrition-information/flax-a-health-and-nutrition-primer/|publisher=Flax Council of Canada |access-date=16 September 2019 |date=2007}}</ref> Plant breeders have developed flaxseed with both higher ALA (70%)<ref name=fcc/> and very low ALA content (< 3%).<ref>{{cite book| editor=Thompson, Lilian U.| editor2=Cunnane, Stephen C.| title = Flaxseed in human nutrition| edition = 2nd| publisher = AOCS Press| year = 2003| pages = 8–11  | isbn = 978-1-893997-38-7}}</ref> The USFDA granted generally recognized as safe (GRAS) status for high alpha linolenic flaxseed oil.<ref>{{cite web |url=http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=grasListing&id=256 |archive-url=https://web.archive.org/web/20091011105715/http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=grasListing&id=256 |url-status=dead |archive-date=October 11, 2009 |title=U.S. FDA/CFSAN Agency Response Letter GRAS Notice No. GRN 00256 |publisher=U.S. FDA/CFSAN |access-date=2013-01-29}}</ref>

==== Nutrient content ====
{| class="wikitable"
|-
! Typical fatty acid content
! % <ref>{{cite web
 | url=http://www.ienica.net/crops/linseed.pdf
 | title=Linseed
 | date=October 14, 2002
 | access-date=2008-01-24
 | publisher=Interactive European Network for Industrial Crops and their Applications
 | archive-url=https://web.archive.org/web/20070927235105/http://www.ienica.net/crops/linseed.pdf
 | archive-date=September 27, 2007
 | url-status=dead
 }}</ref>
! % European<ref name="DGF">Deutsche Gesellschaft für Fettwissenschaft (see 'Leinöl Europa': [http://www.dgfett.de/material/fszus.htm Fettsäurezusammensetzung wichtiger pflanzlicher und tierischer Speisefette und -öle] {{Webarchive|url=https://web.archive.org/web/20081222233514/http://www.dgfett.de/material/fszus.htm |date=2008-12-22 }} (PDF)</ref>
|-
| [[Palmitic acid]]
| 6.0
| 4.0–6.0
|-
| [[Stearic acid]]
| 2.5
| 2.0–3.0
|-
| [[Arachidic acid]]
| 0.5
| 0–0.5
|-
| [[Palmitoleic acid]]
| -
| 0–0.5
|-
| [[Oleic acid]]
| 19.0
| 10.0–22.0
|-
| [[Eicosenoic acid]]
| -
| 0–0.6
|-
| [[Linoleic acid]]
| 24.1
| 12.0–18.0
|-
| [[Alpha-linolenic acid]]
| 47.4
| 56.0–71.0
|-
| Other
| 0.5
| -
|}

Nutrition information from the Flax Council of Canada.<ref name="fcac">{{cite web|url=http://www.flaxcouncil.ca/english/index.jsp?p=g1&mp=nutrition |title=Flax - A Healthy Food |publisher=Flax Council of Canada |access-date=2008-01-24 |url-status=dead |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>

Per 1 tbsp (14 g)
* Calories: 126
* Total [[fatty acid|fat]]: 14 g
* [[Omega-3]]: 8 g
* [[Omega-6]]: 2 g
* [[Omega-9]]: 3 g

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

===Comparison to other vegetable oils===
{{Vegetable_oils,_composition}}

===Additional uses===
{{more citations needed|section|date=January 2021}}
* Animal care products
* [[Bicycle]] maintenance 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 journal| title=Measuring Rate Capability of a Bakelite-Trigger RPC Coated with Linseed Oil| journal= APS Division of Nuclear Physics Meeting Abstracts| pages= DA.033| first= Leah| last= Goldberg| date=2008-10-26| bibcode=2008APS..DNP.DA033G }}</ref>
* [[Textile]]s
* [[Wood preservation#Linseed oil|Wood preservation]] (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|date=2021|title=Fungicidal Efficacy of Drying Plant Oils in Green Beans against Bean Rust (Uromyces appendiculatus)|journal=Plants|language=en|volume=10|issue=1|pages=143|doi=10.3390/plants10010143|pmid=33445566|pmc=7827098|doi-access=free}}</ref>

==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=Ull>{{cite book |doi=10.1002/14356007.a09_055|isbn=3527306730|chapter=Drying Oils and Related Products|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2001|last1=Poth|first1=Ulrich}}</ref>

===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=Ull/> In the [[Medieval era]], linseed oil was boiled with [[lead oxide]] (litharge) to give a product called boiled linseed oil.<ref>{{cite book|title=Medieval and Renaissance Treatises on the Arts of Painting: Original Texts|author=Merrifield, Mary P.|url=https://books.google.com/books?id=C-uiAK74XpsC&q=boiled+linseed+oil+litharge&pg=PR239|isbn=978-0486142241|year=2012|publisher=Dover Publications, Inc.}}</ref>{{page needed|date=July 2017}} 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
  |title=Classic Wood Finishing
  |first=George
  |last=Franks
  |year=1999
  |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 Bat
  |website=Gunn & Moore
  |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}}

== Further reading ==
* {{Cite book
  |title=Staining and Finishing for Muzzleloading Gun Builders 
  |first1=William A.  |last1=Knight 
  |first2=William R.  |last2=Mende 
  |publisher=privately published
  |year=2000
  |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|Linseed oil}}
*{{Cite Collier's|wstitle=Linseed Oil |short=x}}

{{Dietary supplement}}
{{fatsandoils}}

{{Authority control}}

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

[[es:Linaza]]