Mordant

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Mordant

A mordant is a substance used to set dye

Dye

A dye can generally be described as a colored substance that has an Chemical affinity to the Wiktionary:substrate to which it is being applied....
s on fabrics by forming an insoluble compound with the dye. It may be used for dyeing fabrics, or for intensifying stain

Stain

A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. Stains are caused by the chemical or physical interaction of two dissimilar materials....
s in cell or tissue preparations. A mordant is either inherently colloidal or produces colloid

Colloid

A colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. The particles of the dispersed substance are only suspended in the mixture, unlike a solution, where they are completely dissolved within....
s and can be either acid

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ic or alkaline

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
.
ant stain used in Gram's Stain in Microbiology

three methods used for mordanting are:

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Encyclopedia

A mordant is a substance used to set dye

Dye

Stain

Colloid

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ic or alkaline

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
.

Common mordants

Mordants include tannic acid

Tannic acid

Alum

Alum, refers to a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated aluminum potassium sulfate with the chemical formula KAl2.12H2O....
, chrome alum, sodium chloride

Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
, and certain salt

Salt

A salt, in chemistry, is defined as the product formed from the neutralisation reaction of acids and base . Salts are ionic compounds composed of cations and anions so that the product is electrically electric charge ....
s of aluminum, chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-gray, Lustre , hard metal that takes a high polish and has a high melting point....
, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
, iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
, iodine

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
, potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
, sodium

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
, and tin

Tin

Tin is a chemical element with the symbol Sn and atomic number 50. Tin is obtained chiefly from the mineral cassiterite, where it occurs as an oxide, SnO2....
.

Iodine

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
is used as a mordant to set the first dye in gram stains.

Phosphomolybdic acid

Phosphomolybdic acid

Phosphomolybdic acid, also known as dodeca molybdophosphoric acid or PMA is a component of Masson's trichrome stain. It is a yellow-green compound, freely soluble in water and polar organic solvents such as ethanol....
is used as a mordant to set light green when staining with Masson's trichrome stain. Mordant stain used in Gram's Stain in Microbiology

Methods

The three methods used for mordanting are:

Pre-mordanting: The substrate is treated with the mordant and then dyed.
Meta-mordanting: The mordant is added in the dye bath itself.
Post-mordanting: The dyed material is treated with a mordant.

The methods have different effects on the shade
Tints and shades

In color theory, a tint is the mixture of a color with white, which increases lightness , and a shade is the mixture of a color with black, which reduces lightness....
obtained after dyeing and also on the fastness properties. It also depends upon the dye and the substrate. It is therefore necessary to choose a proper method to get the required shade and fastness by optimization of parameters.

Cotton
Cotton

Cotton is a soft, staple fiber that grows in a form known as a boll around the seeds of the cotton plant a shrub native to tropical and subtropical regions around the world, including the Americas, India and Africa....
:

Since metallic mordants are soluble in water and are loosely held by the cotton fibres, these mordants have to be precipitated on the fabric by converting them into insoluble form, or by first treating the fibres with oil or tannic acid

Tannic acid

Tannic acid , a commercial form of tannin, is a polyphenol. Its weak acidity is due to these phenol groups in the structure. Tannic acid is a basic ingredient in the chemical staining of wood....
and then impregnating treated fabric with solution of mordant, whereby the metallic mordants are held on to cotton via oil or tannic acid.

Wool
Wool

Wool is the fiber derived from the specialized skin cells, called follicles, of animals in the Caprinae family, principally domestic sheep, but the hair of certain species of other Mammalia such as cashmere goat, llamas, rabbits and keeshonds may also be called wool....
:

Unlike cotton, wool is highly receptive toward mordants. Due to its amphoteric nature wool can absorb acids and bases equally effectively. When wool is treated with a metallic salt it hydrolyses 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.

Silk
Silk

Silk is a natural protein fiber, some forms of which can be weaving into textiles. The best-known type of silk is obtained from Pupa#Cocoons made by the larvae of the mulberry silkworm Bombyx mori reared in captivity ....
:

Like wool, silk is also amphoteric and can absorb both acids as well as bases. However, wool has thio

Thio

The Prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This meaning is especially valid in organic chemistry....
groups (-SH) from the cystine

Cystine

Cystine is the amino acid dimer formed when a pair of cysteine molecules are joined by a disulfide bond. It is described by the formula 2....
amino acid

Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
, which act as reducing agent and can reduce hexavalent chromium of potassium dichromate

Potassium dichromate

Potassium dichromate, K2Cr2O7, is a common inorganic compound chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications....
to trivalent form. The trivalent chromium forms the complex with the fibre and dye. Therefore potassium dichromate cannot be used as mordant effectively.