The dyeing process involved individual strands left to dry in the open air, exposing them to the elements. This meant that strands had a variation of colour even when they had been dyed in an identical mix. Dyes used in Persian rugs were obtained from plants, animals and insects and recipes for dyes were handed down from generation to generation within families and tribes. We are familiar with cochineal as food colouring for baking, but for centuries the bright red cochineal insect was a staple ingredient in many Persian carpets. The Kermes insect, found in the bark of oak trees, also produced a red hue and is where the word 'crimson' originated. A common Persian plant, madder, provided shades of red, pink or violet depending on how it was treated. Blue was created from the indigo plant, a rotational crop, soaked in water to separate the dye from the plant.
Black is seen in antique rugs less frequently because the process of soaking iron shavings in vinegar, used to obtain the dye, has a corrosive effect on wool. Very rare yellows originated from the familiar cooking spices turmeric and saffron. Cultivated saffron produced a pure yellow, and turmeric root yielded a lighter yellow. An ingredient that is less familiar to us is the mulberry bush. A fungus that grew on the bush was the source of a green-yellow. Other shades were produced by mixing combinations of these with other natural ingredients. For example, brown came from mixing madder with yellow and green walnuts, although this had a tendency to fade as it aged. The very best weavings could also contain substances as exotic gold and silver thread, although these were reserved for the courts and palaces or as gifts for the rulers of neighbouring countries. It is often said that all carpets are perfectly imperfect. Slight inconsistencies show that a rug was woven by hand, moreover the weaver may make an intentional mistake, in line with the belief that only the Supreme Being can make something that is perfect.