The wool can be dyed at any stage of the production - as a fleece, as yarn, or as the finished garment. In ancient sources, some instances occur where the sheep were, it seems, dyed before they were shorn. Pliny the Elder says in his Natural History , "I have, before now, seen the fleeces even of living animals dyed purple, scarlet and crimson as if luxury had compelled them to be born like that" (Pliny p. 126). Most often in ancient Rome, however, the fleece was dyed after it was shorn and before it was spun into yarn.
Through classical authors and textiles that have been preserved,
we know that dyes were used on garments. Though the methods and
chemistry used by Roman dyers is not completely known, we know many
of the dyes that were used in ancient Rome and can conjecture as to
Before many dyes could be applied, a mordant was required. The fiber was treated with alum or iron salts. This made the dyestuffs adhere to the fiber easily. Through the mordants, the shade of the color could be affected.
A much revered dye was a purple dye obtained from the mollusk Murex brandaris . This dye was very expensive because of its rarity. It was necessary to capture many thousands of shellfish for a little of the dyestuff. Purple, therefore, became a royal color long before Roman times. It was declared by both Julius and Augustus Caesar that only the Emperor and his household were allowed to wear the cherished color.
One drop of glandular mucous is extracted from each mollusk. The fluid is at first white, but turns yellow-green on exposure and finally turns to the permanent violet or reddish-purple (Leggett, p. 64-68). Pliny mentions this dye and tells us that salt is added to the dye and left to dissolve for three days. Then the mixture is heated along with water; this helps to skim off any flesh from the mollusks. After about nine days the cauldron is filtered and a washed fleece is dipped for a trial. The liquid is heated. The fleece is soaked for about five hours, carded, and then it is again dipped until it absorbs all of the dye. A blackish color was considered superior to a reddish one (Pliny the Elder, p. 139).
Indigo was also used in Rome by Pliny's lifetime (AD 23-79). In his time, however, indigo referred to any blue pigment that was separated from plants. Today, indigo refers solely to a particular plant. This plant, native to India, is three to five feet in height and has long slender pods and narrow leaves. The dye is found only in the leaf and the amount of dye in each leaf is small. The plant is cut and immediately placed in vats and steeped in water for nine to fourteen hours. The liquid, yellow-orange to olive-green, is exposed to oxidation by air by striking the slime-like substance with strong bamboo sticks, and it gradually changes color to dark green, then finally blue. The mixture is allowed to settle, the top water is drawn off, and the indigo sludge is heated by fire. As it cools, the liquid becomes a paste and this is formed into bars (Leggett, pp. 19-20).
There were cheaper and more readily available vegetable dyes such as madder, a red dye. The root of the madder plant is surrounded by small fibers and is covered with black bark. Most of the pigment is contained in the red mass between the outer skin and heart of the root. Typically, the root was dug out, washed, allowed to dry and ground to a fine powder (Leggett, p. 2-3).
Other dyes used in Rome include saffron which was collected from
the pistils from the autumn crocus. It produced a brilliant yellow
(Brown, p. 248). Weld is another yellow dye source. The Romans
restricted the use of yellow to bridal garments and the garments of
the six Vestal Virgins (Leggett, p.
With the invention of synthetic dyes, we are able to produce a much wider range of color as well as more vibrant and color-fast colors. Synthetic dyes can reproduce the colors from natural dyes as well as hundreds more. The synthetic dyes are inexpensive, not very harmful to wool fiber as some mordants are, quick and easy, and color-fast.