Dyes

DYES

The following list gives a general classification of colouring matters for dyeing textile fibres: - Acid Colours dye animal fibres only and have no affinity for cellulose. If union goods are dyed with acid dyes the cotton remains white and the wool is dyed. They dye wool and silk from baths containing Glauber's salt and some acid, hence their name. Acid colours consist principally of the Azo compounds and are fairly cheap, so are used for the dyeing of dress materials, suitings, etc. No preparation of the fabric is necessary prior to dyeing. Wool and silk fabrics ate simply steeped in a warm acidified solution. Azo Dyes - These are colouring matters used for cotton dyeing and are developed direct on to the fibre. Basic Dyes - Cotton has no direct affinity for basic dyes, which consist of colour bases in combination with other chemicals, as tannic acid, sumach, or other tanning substances. Tannic acid is taken up by cotton which will then absorb the basic colours. They are very bright but not very fast. They dye wool and silk direct from plain baths. Developing Colours - See Developing Colours. Direct Cotton Colours - Dye cotton, linen, wool or silk directly, will dye cotton direct but by the addition of various salts deeper shades are obtained. With the addition of a little acid will dye wool and silk. See direct Dyes. Mordant Colours - As a rule these are very fast to washing and mostly fast to; light, such as logwood, black, Turkey red, etc. The mordant forms insoluble compounds with the colours, which are then applied to the fibres so that the insoluble coloured compounds are formed within the fibres The cotton is prepared first with some metallic mordant, as chrome, iron or alumina. Substantive Dyes - Have the property of dyeing fibres direct. They are Direct Dyes, that is they have an affinity for fibres. Sulphur and vat dyes are substantive towards cotton. Sulphur Colours are used for vegetable fibres only. These colours are insoluble in water and require the addition of sodium sulphide which converts them into soluble substances which will dye cotton. Usually fast to washing and alkalis - not so fast to bleaching (see Sulphur Colours). Vat Colours - These are fast dyes for cotton. They are insoluble in water so are converted into a soluble compound by some chemical reducing agent, and then they have a direct affinity for cotton which is dyed when immersed in the solution. There are two main classes, those prepared from anthraquinone and those related to indigo. They will dye viscose and cuprammonium rayons (see Vat Dyes)