DYES AND DYEING - Archaeological Chemistry - page 365

14

DYES AND DYEING

Dyes , often also called coloring matters or colorants , are intensely colored,
soluble organic substances used to impart color to fibrous materials (see
Textbox 66). Not all colored and soluble organic substances, however, are
dyes; only those whose molecules have a considerable structural complex-
ity are useful for imparting color to other materials. Moreover, a substance
is considered a dye only if the color it imparts is fairly permanent , that is,
resistant to fading and disappearance.
The use of dyes seems to have began over 10 millennia ago, when dyes
of vegetable origin were apparently applied to the skin simply for amuse-
ment, for ritual purposes, or to identify or differentiate status or social group.
All the dyes used in the past and up to the nineteenth century, when artifi-
cial dyes were first synthesized, were of natural origin; most were extracted
from plants, some from animals (Verhecken 2005). Common dyes well
known since antiquity are listed in Table 92 (Kirby 1988; Celoria 1971).

14.1. STAINS AND STAINING

Sometimes, inorganic substances such as, for example, some mineral
pigments , have been used to color fibrous materials, a process generally
referred to as staining . Pigments are not soluble in water, the almost univer-
sal solvent used for dyeing, nor do they react with the fibrous substrate. They
generally become attached to the substrate by a binder, and the words stain
and staining imply that the pigment (the coloring matter) simply becomes
attached to the substrate. Table 93 lists mineral stains that, dispersed in
water, have been used for staining fibrous materials.