Natural dyes are a class of colorants extracted from vegetative matter and animal residues.
Historically, natural dyes were used to color clothing or other textiles, and by the mid-1800’s chemists began producing synthetic substitutes for them. By the early part of this century only a small percentage of textile dyes were extracted from plants. Lately there has been increasing interest in natural dyes, as the public becomes aware of ecological and environmental problems related to the use of synthetic dyes. Use of natural dyes cuts down significantly on the amount of toxic effluent resulting from the synthetic dye process.
Natural dyes generally require a mordant, which are metallic salts of aluminum, iron, chromium, copper and others, for ensuring the reasonable fastness of the color to sunlight and washing. Customers who have become accustomed to the dazzling colors and wash and light fastness of synthetic dyes are hard to convince, as only a few of the natural dyes have good all round fastness
Quality standards for natural dyes vary widely. The problem arises with standardization of the colors as no two dye lots are identical. While paint manufacturers might be interested in the uniqueness of each batch of color produced, technicians in the pharmacology, food and textile industry loathe this lack of consistency.
This latter group has attempted to standardize natural dyes by imposing a color index that attempts to classify and name them. Each dye is thus named according to the following pattern:
natural + base color + number
These dyes are thereby specifically identified as dyes of the stated colour, but it does not specify whether the dyes are derived from animals or plants. This is because it is a classification based on the dye's source and color, and it contains no chemical information, nor does it imply that dyes with similar names but unique numbers are in any way related. It also gives no information about the mechanism by which staining occurs. This is done in order to authenticate the synthesized organic dyes along with natural dyes under the same universal classification system.
Some examples include carmine which comes from cochineal (natural red 4), lac (natural red 25) and hematein which comes from the logwood tree (natural black 1).