Vat dyes are a class of
dye
A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...
s that are classified as such because of the method by which they are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. The original vat dye is
indigo
Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', ...
, once obtained only from plants but now often produced synthetically.
Materials suited for vat dyeing
Although almost all dyeing can be done in a vat, the term vat dye is used to describe a chemical class of dyes that are applied to cellulosic fibre (''i.e.'', cotton) using a redox reaction as described below. Because of the use of caustic soda, and the very high pH of the dye bath in the dyeing process, wool cannot be dyed using vat dyestuffs. This is because wool is soluble in caustic soda solutions. Instead, it is possible to dye wool at room temperatures with indigo (vat blue 1) and other low substantive vat dyes using
soda ash
Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
as the alkali source with very little strength loss. Vat red 10, vat violet 13 and
vat orange 1 can be applied in this manner as well.
[''The Chemistry of Vat Dyes'' by Dianne Epps]
Dyeing process
Vat dyes characteristically require a
reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth met ...
to
solubilize
Micellar solubilization (solubilization) is the process of incorporating the solubilizate (the component that undergoes solublization) into or onto micelles. Solublization may occur in a system consisting of a solvent, an association colloid (a co ...
them. The most common reducing agent is
sodium dithionite (Na
2S
2O
4), which converts the dye to its "
leuco" form that is soluble. Once attached to the fabric, the leuco dye is then oxidized to the insoluble state which is intensely colored.
Chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s such as
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
,
reduction,
pH control are often necessary; even the dissolution process necessitates measuring out appropriate quantities of
caustic soda
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
and
sodium hydrosulphite in order to achieve reduction. The dye is soluble only in its reduced form. The fiber is immersed repeatedly in this oxygen-free dyebath, then exposed to the air, whereupon the
water-soluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solub ...
reduced form changes color as oxygen turns it to the water-insoluble form. For these reasons, vat dyes are less suitable than fiber-reactive dyes for amateur use.
Indigo
Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', ...
is an example of this dye class: it changes from yellow, in the dyebath, to green and then blue as the air hits it.
Not all vat dyeing is done with vat dyes.
Properties
The vat dyes have high
color fastness
Colour fastness is a term—used in the dyeing of textile materials—that characterizes a material's colour's resistance to fading or running. Colour fastness is the property of dyes and it is directly proportional to the binding force between pho ...
, which is uncommon in other dye classes. On the other hand, vat dyes tend to have poor rubbing fastness, but this can be mitigated with special treatments to the fabric. Indigo is subject to major crocking (i.e., rubbing the dye off onto other items) unless it is applied carefully. This means that dipping many times in a weaker dye-bath is more preferred than to dip once in a stronger dye-bath.
Light-oxidized vat dyes
Inkodye is a type of vat dye that uses
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
rather than oxygen to "fix" the dye, with a wide variety of possible effects. These dyes, which are chemically similar to vat dyes, are developed by light instead of being applied in an oxygen-free bath and being developed in the fabric by exposure to oxygen. Inkodyes are true dyes, not fabric paints. A dye itself attaches to the fabric; fabric paint includes a glue-like binder, which imparts a stiffer feeling to the fabric.
Chemical structures
For example, vat blue 2 and 3 are halogenated or methylated derivatives and so are several violets. Many other vat dyes are derivatives of
anthroquinone
Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoan ...
s.
File:Indigo skeletal.svg, Vat Blue 1
File:Indanthren.svg, Vat Blue 4
File:Vat Blue 20.png, Vat Blue 20
File:Vat Blue 21.png, Vat Blue 21
File:Vat Blue 25.png, Vat Blue 25
File:Vat Blue 26.png, Vat Blue 26
File:Vat Blue 30.png, Vat Blue 30
File:Vat Blue 36.svg, Vat Blue 36
Vat Blue 36 is a vat dye that is chemically related to indigo. It is produced by condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most ofte ...
File:Vat Blue 64.png, Vat Blue 64
File:Vat Green 1.svg, Vat Green 1
File:VatGreen3.png, Vat Green 3
File:VatGreen8.png, Vat Green 8
File:Vat Green 9.svg, Vat Green 9
Vat Green 9 is a green colored vat dye. It is derived from violanthrone
Violanthrone, also known as dibenzanthrone, is an organic compound that serves as a vat dye and a precursor to other vat dyes. X-ray crystallography confirms that the molecu ...
File:VatGreen11.png, Vat Green 11
File:VatGreen12.png, Vat Green 12
File:VatOrange1.png, Vat Orange 1
File:VatOrange2.png, Vat Orange 2
File:VatOrange3.svg, Vat Orange 3
File:VatOrange9.png, Vat Orange 9
File:VatOrange15.png, Vat Orange 15
File:VatOrange17.png, Vat Orange 17
File:Vat violet 15.png, Vat violet 15
File:VatViolet18.png, Vat Violet 18
File:VatRed10.png, Vat Red 10
File:VatRed13.png, Vat Red 13
File:VatRed18.png, Vat Red 18
File:VatRed28.png, Vat Red 28
File:Vat Red 29.png, Vat Red 29
File:Vat Brown 1.png, Vat Brown 1
File:Vat Brown 3.png, Vat Brown 3
File:Vat Brown 45.png, Vat Brown 45
File:Vat Black 25.png, Vat Black 25
File:Vat Black 27.png, Vat Black 27
File:Vat Black 29.png, Vat Black 29
File:Vat Yellow 1.svg, Vat Yellow 1
Vat Yellow 1 is a vat dye, yellow in appearance under some conditions used in cloth dyeing. Its synonyms are flavanthrone and Indofast Yellow, and it is in the class of anthraquinone
Anthraquinone, also called anthracenedione or dioxoanthracene, ...
File:Vat Yellow 4.png, Vat Yellow 4
A value-added tax (VAT), known in some countries as a goods and services tax (GST), is a type of tax that is assessed incrementally. It is levied on the price of a product or service at each stage of production, distribution, or sale to the end ...
File:Vat Yellow 10.png, Vat Yellow 10
File:Vat Yellow 12 corrected.png, Vat Yellow 12
File:Vat Yellow 20.png, Vat Yellow 20
File:Vat Yellow 28.png, Vat Yellow 28
References
''Imagery on Fabric'' by Jean Ray Laury
External links
Inkodye - Light-sensitive vat dye*
Reactive Dye Application techniques
{{Dyeing