Mordanting

To make the colors bright and fast, natural mordants (an element which aids the ehemical reaction so that the fibre absorbs the dye, preventing the colour from either fading with exposme to light or washing out) sueh as Myrballams, rhubarb leaves, oils, minerals, alum, iron Vat, etc., are used. No heavy metal mordants like copper, chrome, zinc, tin, etc., have been used. 

Herbal dyes or as in Wikipedia Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources - roots, berries, bark, leaves, and wood -and other organic sources such as fungi and lichens. These have considerate advantage over conventional dyes, where various 8000 chemicals are known to be used in textiles industry for getting today s vibrant colors. 

Turmeric is a great example of a natural dye used in Asia for many years, and it is a fantastic herb to treat small euts and wounds. It is actually an antiseptic and anti-inflammatory herb, whieh means that you can stick it right into your first-aid kit. Turmeric is an ideal dye for fabrics that touch the skin of people, especially those allergic to fabrics dyed conventionally and infused with chemicals. 

Medicinally rich herbal formulations using plant material, minerals and oils like, turmeric, Myraballm, castor oil, sea salt, etc., are used for dyeing of the fabric or yam. The medicinal qualities of the herbs are retained by immersing the plant material directly in the dye bath. 

The cloth does not lose its medicinal effect even after constant use since the medical dyes (herbs) go into the yam itself. The yam is dipped into the herbs and the fabric is dipped again. 

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Mordant acid dyes combine simultaneously with the mordanting agent (generally Cr(OH)j) and the fibre the dyestuff generally contains ortho OH -azo or OH-OH groups. 

Dissolves in alkaline solutions to give purple-red solutions which are precipitated as lakes by heavy metal salts. Occurs naturally as a glucoside in madder but produced synthetically by fusing anthraquinone-2-sulphonic acid with NaOH and some KCIO3. Applied to the mordanted fibre. Al(OH)3 gives a bright red lake, Cr(OH)3 a red lake, FefOH) ... 

Bismarck brown, Basic Brown 1 Basic azo-dyestuff, dyes wool (reddish brown), used for cotton with tannin as mordant. Used as hair dye. 

Na COj and Na2S with SO2 or from Na2S03 plus sulphur. Forms many hydrates. Used-in photography ( hypo ) because it dissolves silver halides. Also used in tanning, preparation of mordants, as a fermentation preventative in dyeing and in chemical manufacture. 

Tin(ll) chloride, SnCl2, stannous chloride. M.p. 247 - C. While solid (Sn plus gaseous HCl), forms hydrates (SnCl2,2H20 is tin salt) from Sn and aqueous HCl. Acts as acceptor in complexes and forms complexes with transition metals. Used as a mordant. 

Tin IV) chloride, SnCU, stannic chloride. M.p. — 33" C, b.p. 1I4°C. Colourless fuming liquid (Sn plus CI2) hydrolysed in water but forms SnCl4,5H20 and [SnCl p" from acid solutions, soluble in organic solvents. Used as a mordant. 

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

Salts of this acid are known and ammonium hexachlorostan-nate(IV) (NH4)2SnCb, is used as a mordant. 

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

Chromium(III) hydroxide, like aluminium hydroxide, possesses adsorptive power, and the use of ehromium compounds as mordants is due to this property. 

L. alumen, alum) The ancient Greeks and Romans used alum as an astringent and as a mordant in dyeing. In 1761 de Morveau proposed the name alumine for the base in alum, and Lavoisier, in 1787, thought this to be the oxide of a still undiscovered metal. 

Other compounds are of industrial value lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum. 

Most xanthene dyes are classified as basic dyes by their method of appHcation acid dyes can be produced by introduction of sulfonic acid groups. The fluoresceins, which contain carboxy and hydroxy substituents, are also acid dyes for coloration of silk. Some of the fluoresceins in which the carboxy group has been esterified, are soluble in alcohol or other organic solvents and can be classified as solvent dyes. Mordant dyes can be produced by introducing o-dihydroxy or sahcyhc acid groups (2), which when metallised can have very good lightfastness. 

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