Pigment, Dyestuffs and types of dyes

Pigment is a material that changes the colour of the light it reflects as the result of selective colour absorption. Pigment generally is insoluble, and has no affinity for the substrate.

Dyestuffs can be described as a coloured substance that has an affinity to the substrate to which it is being applied.

Types of dyes:

1. Acid dyes are water soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dyebaths.

2. Basic dyes are water soluble cationic dyes that are mainly applied to acrylic fibers.Usually acetic acid is added to the dyebath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of paper.

3. Direct or substantive dyeing is normally carried out in neutral or slightly alkaline dyebath, at or near boiling point, with the addition of either Sodium Chloride or Sodium Sulfate. Direct dyes are used on cotton, paper, leather, wool, silk and nylon.

4. Mordant dyes require a mordant, which improve the fastness of the dye against water, light and perspiration. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool.

5. Vat dyes are essentially insoluble in water and incapable of dyeing fibers directly. However, reduction in alkaline liquour produces the water soluble alkali metal salt of the dye, which in this leuco form, has an affinity for the textile fiber. Subsequent oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.

6. Reactive dyes utilize a chromophore attached to a substituent that is capable of directly reacting with the fibre substrate. The covalent bond that attach reactive dye to natural fibers make them among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibaron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are far the best choice for dyeing cotton and other cellulose fibers.

7. Disperse dyes were originally develop for the dyeing cellulose acetate, and are substantially water insoluble. The main use is to dye polyester.

8. Azo dyeing is a tecnique in which an insoluble azoic dye is produced directly onto or within the fibre.

9. Sulfur dyes are two part 'developed' dyes used to dye cotton with dark colors. The initial bath imparts a yellow or pale chartreuse color.