Natural colorants fall into three categories, according to the techniques for using them - mordant dyes, vat dyes and direct dye.
This is the largest category. Without a mordant these dyes can not, or can do so on slightly, and the fixing action of a mordant is essential if the dye is to take. Mordants may be used before, during or subsequent to dyeing. When they are used both before and after the dyeing process, the resultant color will be stronger. The mordant alum (potassium aluminum sulphate) is most commonly used as it gives the brightest colors.
The most important of these is indigo. Vat dyes are not soluble in water, but can be brewed in an alkaline liquid in a sealed container, or vat, to produce a liquor in which the dye is present as a colorless salt. Urine is often used to make the indigo brew, so the liquor is yellow. It is diluted for dyeing and no blue color appears until the yarn is removed from the dyebath. Contact with air reverses the original brewing reaction, precipitating indigo onto the fibres.
As the name suggests, direct dyes color the fibre without a mordant or vatting. Walnut husks and leaves provide direct dyes that produce various shades of brown. Madder can also be used without a mordant.
Natural colourants categories
One of the most important visual factors of carpet is color. Generally, chromogenic substances can be categorized as follows :
1- Pigments :
These are soluble in organic solvents and are not used in dyeing.
2- Chromatins (bases) :
Chromatic substances absorbed by materials either via the absorbtion phenomenon or through diffusion (penetration). They are soluble in water and are divided into two natural and chemical types.
Natural dye colours are derived from the following elements: