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Tyrian purple (Greek: πορφύρα, porphura), also known as royal purple or imperial purple, is a purple-red dye made by the ancient Canaanites/Phoenicians in the city of Tyre, from a mucus-secretion of the hypobranchial gland of a marine snail known as the Murex brandaris or the Spiny dye-murex.
The Phoenicians also made a purple-blue indigo dye, called royal blue or hyacinth purple, which was made from a related species of marine snail, called the Murex trunculus or the Banded dye-murex.
Tyrian purple was expensive: the fourth-century BC historian Theopompus reported, "Purple for dyes fetched its weight in silver at Colophon" in Asia Minor.[1]
The fast, non-fading dye was an item of luxury trade, prized by Romans, who used it to colour ceremonial robes.
Pliny the Elder described the dyeing process of two purples in his Natural History - ... the Tyrian hue ... is considered of the best quality when it has exactly the colour of clotted blood, and is of a blackish hue to the sight, but of a shining appearance when held up to the light; hence it is that we find Homer speaking of "purple blood."
The peoples of Crete, Tyre, Sidon, and other sites on the Mediterranean apparently obtained the dye from three species of marine mollusks, Murex brandaris, Murex trunculus, and Thais haemastoma. The Tyrians used M. brandaris mostly, while M. trunculus was the principal source for most of Sidonian dyes. The fluid containing the dye is produced by a gland located in the mantle cavity of the snail between the rectum and the gills, and when first exuded it is a colorless or milky fluid. Huge quantities of the glands of larger specimens and of whole smaller specimens, ground up, were placed in vats with salt added to slow decomposition and exposed to sunlight for two to three days. The dye changes under the influence of direct sunlight, first becoming yellow, then passing through pale-green shades to bluish, and finally turning red-purple. Next the material was diluted five or six times with water and boiled at a moderate rate for ten days. At the end of this period, the strength of the dye was tested by soaking pieces of wool in the fluid for five hours.Reddish-purple dye is most readily obtainable from the Murex brandaris and Thais haemastoma as opposed to the bluish-purple obtained from the Murex trunculus. The photo-chemical properties of the trunculus dye occurst when the dye is in a reduced state (a prerequisite for dyeing wool), exposure to ultra-violet light transforms the blue-purple colorant (dibromoindigo) to unadulterated blue (indigo).
The main chemical constituent of the Tyrian dye was discovered by Paul Friedländer in 1909 to be 6,6′-dibromoindigo, a substance that had previously been synthesized in 1903. However, it has never been synthesized commercially.
Mexican and South American natives still prefer the molluscan dyes for their garbs, since they produce more natural - looking and traditional hues. In Oaxaca, the Mixtec search the seashore for the Purpura patula pansa (Gould, 1853 - the "Wide-mouthed Purpura"), squeeze some of their juices onto yarns, and return the shell to its home, to be used again the following season. These same dyes were used as early as 400 BC.