View source for Mordant

{{short description|Substance used for binding dyes to fabrics}}
{{about|the substance used to set dyes|the musical ornament|Mordent}}
{{Other uses}}
{{anchor|top|dye fixative}}
[[File:Mordant red 19.png|thumb|200 px|[[Mordant red 19]] is a typical mordant dye.  Like many mordant dyes, it features the [[azo group]] (RN=NR) and various sites for [[chelating agent|chelating to metal cations]].]]
[[File:Indienne, Wesserling.JPG|thumb|A French ''[[Indienne]]'', a printed or painted textile in the manner of Indian productions, which used mordants to fix the dyes]]
A '''mordant''' or '''dye fixative'''<!-- more modern parlance? Now redirects here ---> is a substance used to set (i.e., bind) [[dye]]s on fabrics. It does this by forming a [[coordination complex]] with the dye, which then attaches to the fabric (or tissue).<ref name="Gold">{{GoldBookRef|title=mordant|file=M04029}}</ref> It may be used for dyeing fabrics or for intensifying [[stain]]s in [[biological specimen|cell or tissue preparation]]s. Although mordants are still used, especially by small batch dyers, they have been largely displaced in industry by [[substantive dye|direct]]s.<ref name=Azodye>{{cite book|last1=Hunger |first1=Klaus|last2=Mischke |first2=Peter |last3=Rieper |first3=Wolfgang |last4=Zhang |first4=Shufen}|title=Azo Dyes, 5. Developing Dyes |date=March 8, 2019 |url=https://onlinelibrary.wiley.com/doi/10.1002/14356007.o03_o09.pub2 |work=[[Ullmann's Encyclopedia of Industrial Chemistry]] |pages=1–19 |place=Weinheim, Germany |publisher=[[Wiley-VCH Verlag]] GmbH & Co. KGaA|doi=10.1002/14356007.o03_o09.pub2 |isbn=9783527306732 |access-date=|oclc=46878292}}</ref>
The term mordant comes from the Latin ''mordere'', "to bite". In the past, it was thought that a mordant helped the dye "bite" onto the fiber so that it would hold fast during washing. A mordant is often a [[polyvalency (chemistry)|polyvalent]] [[metal]] [[ion]], and one example is [[chromium]] (III).<ref name="Stainsfile - How Stains Work">{{Cite news |url=//stainsfile.info/StainsFile/theory/mordant.htm |title=Stain Theory – How mordants work |last=Llewellyn |first=Bryan D. |date=May 2005 |url-status=dead |archive-url=https://web.archive.org/web/20160520064357/http://stainsfile.info/StainsFile/theory/mordant.htm|archive-date=May 20, 2016 }}</ref> The resulting coordination complex of dye and ion is [[colloidal]] and can be either [[acid]]ic or [[base (chemistry)|alkaline]].
==Common dye mordants==
Mordants include [[tannic acid]], [[oxalic acid]],<ref>{{cite book |last=Von Wagner |first=Rudolf |url=http://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t3tt4gz1p;view=1up;seq=527 |title=Manual of chemical technology |publisher=D. Appleton & Co. |year=1897 |location=New York |page=499}}</ref> [[alum]], [[chrome alum]], [[sodium chloride]], and certain [[salt (chemistry)|salt]]s of [[aluminium]], [[chromium]], [[copper]], [[iron]], [[iodine]], [[potassium]], [[sodium]], [[tungsten]], and [[tin]].
Iodine is often referred to as a mordant in [[Gram staining|Gram stains]], but is in fact a trapping agent.<ref name="Stainsfile - How Stains Work"/>{{failed verification|date=November 2024}}
==Dyeing methods==
[[File:Dye rot.jpg|thumb|Dye rot from iron mordant]]
The three methods used for mordanting are:
* Pre-mordanting (onchrome): The substrate is treated with the mordant and then the dye.  The complex between the mordant and dye is formed on the fibre.
* Meta-mordanting (metachrome): The mordant is added in the dye bath itself.  The process is simpler than pre- or post-mordanting, but is applicable to only a few dyes.  Mordant red 19 shown above is applied in this manner
* Post-mordanting (afterchrome): The dyed material is treated with a mordant.  The complex between the mordant and dye is formed on the fibre.
The type of mordant used affects the [[Tints and shades|shade]] obtained after dyeing and also affects the fastness property of the dye.  The application of mordant, either pre-mordant, meta-mordant or post-mordant methods, is influenced by:
* The action of the mordant on the substrate: if the mordant and dye methods are harsh (for example, an acidic mordant with an acidic dye), pre-mordanting or post-mordanting limits the potential for damage to the substrate.
* The stability of the mordant or dye lake or both: the formation of a stable dye lake means that the mordant can be added in the dye without risk of losing the dye properties (meta-mordanting).
Dye results can also rely on the mordant chosen as the introduction of the mordant into the dye will have a marked effect on the final color. Each dye can have different reactions to each mordant. For example, [[cochineal]] scarlet, or Dutch scarlet as it came to be known, used cochineal along with a tin mordant to create a brilliant orange-hued red.<ref>Phipps, Elena (2010). ''Cochineal Red The Art History of a Color'', p34. Yale University Press, New Haven and London. {{ISBN|978-0-300-15513-6}}.</ref>
Residual iron mordant can damage or fade fabric, producing "dye rot".<ref>{{Cite web |url=http://www.quilthistory.com/cleaning.htm |title=Quilt History- informational site about antique quilts and vintage textiles including article and an interactive chat group |access-date=2012-01-29 |archive-date=2012-12-21 |archive-url=https://web.archive.org/web/20121221111851/http://www.quilthistory.com/cleaning.htm |url-status=dead }}</ref>
===Dye lake===
The [[Lake pigment|dye lake]] is an insoluble complex formed upon combining the dye and mordant, which then attaches to the substrate. Mordants increase the fastness of the dye since the higher molecular weight dye is now bonded to the fibre.<ref name="Stainsfile - How Stains Work"/>
The type of mordant used can change the colour of both the dye-plus-mordant solution and influence the shade of the final product.
===Wool===
Unlike cotton, [[wool]] is highly receptive toward mordants. Due to its [[amphoteric]] nature wool can absorb acids and bases with equal efficiency. When wool is treated with a metallic salt it [[hydrolyse]]s the salt into an acidic and basic component. The basic component is absorbed at –COOH group and the acidic component is removed during washing. Wool also has a tendency to absorb fine precipitates from solutions; these cling to the surface of fibres and dye particles attached to these contaminants result in poor rubbing fastness.
[[File:Congo-red-2D-skeletal.png|thumb|322px|The discovery of [[Congo red]] in 1883, followed by many other synthetic [[azo dye]]s, heralded the demise of mordant dyes.]]
===Silk===
Like wool, [[silk]] is also amphoteric and can absorb both acids and bases. However, wool has [[Thio-|thio]] groups (-SH) from the [[cystine]] [[amino acid]], which act as reducing agent and can reduce [[hexavalent]] chromium of [[potassium dichromate]] to [[trivalent]] form. The trivalent chromium forms the complex with the fibre and dye. Therefore, potassium dichromate cannot be used effectively as mordant.
===Animal and plant tissues===
In [[histology]], mordants are indispensable in fixing dyes to tissues for [[Microscopy|microscopic examination]].
Methods for mordant application depend on the desired stain and tissues under study; pre-, meta- and post-mordanting techniques are used as required.
The most commonly used stain used in diagnostic histology of animal tissues is Harris' [[haematoxylin]] as part of a haematoxylin and eosin [[H&E stain|(H&E)]] stain.
==References==
{{reflist}}
== Further reading ==
* {{Cite book|url=https://books.google.com/books?id=OTEREwtL6dIC&q=Mordant&pg=PA69|title=A Weaver's Garden: Growing Plants for Natural Dyes and Fibers|last=Buchanan|first=Rita|date=1999|publisher=Courier Corporation|isbn=9780486407128|language=en}}
* {{Cite book|url=https://books.google.com/books?id=HnSlynSfeEIC&q=Mordant&pg=PA236|title=Prehistoric Textiles: The Development of Cloth in the Neolithic and Bronze Ages with Special Reference to the Aegean|last=Barber|first=E. J. W.|date=1991|publisher=Princeton University Press|isbn=069100224X|language=en}}
==External links==
* [http://griffindyeworks.com/understanding-mordants/ Griffin Dyeworks: Understanding mordants and modifiers]
{{Dyeing}}
[[Category:Dyes]]
[[Category:Printing]]
[[Category:Printmaking]]
[[Category:Electronics manufacturing]]