BY: PRABHAT KHARE

Asst. Professor

Natural Dyes

Nature, has a wonderful visual device for sensing the seven shades of the colour spectrum. Hence, it is considered as the most abundant source of colours.

They play a significant role in man's individual and social life

Archeological findings have shown that natural colours were being used in dyeing, printing, painting and preparing cosmetics among primitive communities throughout the world.

The earliest written record found in China around 2600 B.C.

In the ancient civilization of Greece, Egypt and in the far east, colours had an important place in life.

In the early sixteenth century France, Holland and Germany began to cultivate dye plants as an industry

In 1321, Brazil woad (Isatis tinctoria) was first mentioned as a dye source from East Indies.

HISTORY OF DYES

Dyeing of fibers has been carried out since antiquity. Virtually every culture has its own set of dyestuffs.

Development of synthetic dyes replaced almost all forms of natural dyes with better quality materials as they are more stable.

Natural dyes are still in use but mostly limited to food stuff.

Several dyes from animals have also been used. Cochineal (Coccus cacti) is a scale insect that feeds on cacti Opuntia species.

INTRODUCTION

Paradox: We associate plants with beautiful colors, yet most plant pigments do not make good dyes

Resolution: Most plant pigments are chemically instable – when removed from the environment of the plant cell they are quickly degraded or washed away.

So Dyes:

must be chemically stable (many oxidize when exposed to air)

Dyes must adhere to the fibers or they will be washed out. It is easier to dye animal fibers than plant fibers.

Although many plant parts are colored, the components of some of these parts are not particularly stable and decompose too quickly to be useful. Some do not bind well to the fibers.

In some cases, the dyestuffs bind tightly by chemical bonding and in others they are only bound by hydrophobic interactions.

Chemistry of Dyes

Characterized by their ability to absorb visible part of the electromagnetic spectrum [400-700 nm].

Must have high enough absorption coefficient i.e. how tightly the colour bind to material (10 000 to 40 000 .mol-1.cm-1 ).

As a rule, colorants nowadays have to be harmless.For most natural dyestuffs to be effective, the

article to be coloured must first be saturated with a fixer or mordant

Can be Subdivided on basis of: Colour produce chemical composition or structure, biological function in plant/organism (chlorophyll,

hemoglobin …), physical properties (solubility), Source.

COLOURANTS

MORDANTS (Colour Fixer)As early as the Egyptians, it was known that other substances caused some dyes to bind that normally would not. These are called mordants.

Mordants are chemical additives that sometimes help a fiber accept a dye that it might otherwise reject. (The word mordant comes from the Latin "morders" which means "to bite")

Many mordants are metal salts that appear to form metal bridges between the dye and the fiber molecules.

Sometimes mordants came from the container in which the dyeing was being done and at other times from dung, urine or other compounds added.

Some dyestuffs (such as madder) contain substances that naturally act as mordants.

Few Examples………

PlantsAnimal (eg. Orchil linches, butterfly wings, cochineal insect)

Mushrooms (eg. Democybe, Thelephora)

Mineral (eg. Ocher, caramel)

Classification of NATURAL DYES

Woad, (Isatis tinctoria, Brassicaceae)Woad (Isatis tinctoria,

Brassicaceae or Cruciferae) was widely grown and utilized as a dyestuff in Europe.

Woad contains a smaller amount of the same compounds as found in indigo.

The leaves were crushed and made into balls which were then allowed to ferment. After fermentation, the product was allowed to dry and then re-fermented before use to make it soluble.

One of most important dyestuffs; used as far back as 6000 years in China.

It become an important item of trade between India and other parts of the world by 300 B.C.

Indigo produces an intense deep blue color. The leaves and branches of the plant are harvested, placed in a vat, covered with water, and permitted to ferment.

The sludge of partially rotted plant material which settles to the bottom is collected and pressed into cakes.

When dry, these cakes produce a powder that makes a colorless solution.

Indigo (Indigofera tinctoria, Fabaceae)

When the fabric is first removed from the bath of indigo dye, it is not blue, but turns

blue upon oxidation by air.

This dye was introduced into Europe in the late Middle Ages.

The color of the British soldier's uniform in the Revolutionary War was produced by madder.

sometimes called Turkey red.The dyestuff is found in the root of the plant. (ruberythric acid)

Changing the mordant can give red, pink, lilac, orange, black, and brown colored pigments.

Alizarin (a compound derived from madder) is usually used with an aluminum mordant.(Also used as a biological stain.)

Madder (Rubia tinctoria, Rubiaceae)

Henna (Lawsonia inermis, Lythraceae)

By 3000 B.C., Greek women used henna (Lawsonia inermis, Lythraceae) to dye their hair.

The leaves are ground into a paste that has a great affinity for protein.

Henna is still used in hair preparations.

Dyeing the skin with henna is practiced in many Near Eastern countries.

Achiote or annatto, Bixa orellana, Bixaceae

The plant is probably native to Brazil.

Used by the Aztecs and Mayans for food preparation.

The pulp surrounding the seeds contains a lipid dye that is soluble in grease and dyes foods a yellow-orange-red color.

Achiote is widely used in Latin America, but also in other parts of the world today.

Achiote contains about 2% vitamin A.

Genipapo, (Genipa americana, Rubiaceae)• Genipapo or genipa was used to paint the bodies of many Central and South American Indian groups (tattoos / body art). • The fruit also is eaten.