Tyrian purple (Greek: πορφύρα, porphyra, Latin: purpura), also known as royal purple, imperial purple or imperial dye, is a purple-red dye which was first produced by the ancient Phoenicians in the city of Tyre.
The dye substance occurs naturally, but must be harvested by humans. It consists of a fresh mucous secretion from the hypobranchial gland of a medium-sized predatory sea snail, the marine gastropod Murex brandaris, currently known as Haustellum brandaris (Linnaeus, 1758). This species is commonly called the spiny dye-murex, and it is a species in the family Muricidae, the murex or rock shells. The current range for this species is the "central and western Mediterranean"
In Biblical Hebrew, which like Phoenician is a dialect of Canaanite, the Tyrian purple-red dye extracted from the Murex brandaris is known as shani שָׁנִי [ʃɔni], but usually translated as 'scarlet'. Another dye extracted from a related sea snail, Hexaplex trunculus, could produce a purple-blue color called argaman אַרְגָּמָן [argɔmɔn] (translated 'purple') when processed in shade, or a sky-blue indigo color, called tekhelet תְּכֵלֶת [təxelɛθ] (translated 'indigo') when processed in sunlight (see Photochemistry).
Many other species worldwide within the family Muricidae, for example Plicopurpura pansa (Gould, 1853), from the tropical eastern Pacific, and Plicopurpura patula (Linnaeus, 1758) from the Caribbean zone of the western Atlantic, can also produce a similar substance (which turns into an enduring purple dye when exposed to sunlight) and this ability has sometimes also been historically exploited by local inhabitants in the areas where these snails occur. (Some other predatory gastropods, such as some wentletraps in the family Epitoniidae, seem to also produce a similar substance, although this has not been studied or exploited commercially.)
In nature the snails use the secretion as part of their predatory behaviour and as an antimicrobial lining on egg masses. The snail also secretes this substance when it is poked or physically attacked by humans. Therefore the dye can be collected either by "milking" the snails, which is more labor intensive but is a renewable resource, or by collecting and then crushing the snails completely, which is destructive.
The Phoenicians established an ancillary production facility on the Iles Purpuraires at Mogador, in Morocco. The gastropod harvested at this western Moroccan dye production facility was Phyllonotus trunculus also known by the older name Murex trunculus (Linnaeus, 1758)).
This second species of dye murex currently occurs on "the Mediterranean and Atlantic coasts of Europe and Africa (Spain and Portugal, Morocco, and the Canary Islands"
The fast, non-fading dye was an item of luxury trade, prized by Romans, who used it to colour ceremonial robes. It is believed that the intensity of the purple hue improved, rather than faded, as the dyed cloth aged. 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."
Archaeological data from Tyre indicate that the snails were collected in large vats and left to decompose. This produced a hideous stench that was actually mentioned by ancient authors. Not much is known about the subsequent steps, and the actual ancient method for mass-producing the two murex dyes has not yet been successfully reconstructed; this special "blackish clotted blood" colour, which was prized above all others, is believed to be achieved by double-dipping the cloth, once in the indigo dye of H. trunculus and once in the purple-red dye of M. brandaris.
The Roman mythographer Julius Pollux, writing in the second century BC, asserted (Onomasticon I, 45–49) that the purple dye was first discovered by Heracles, or rather, by his dog, whose mouth was stained purple from chewing on snails along the coast of the Levant. Recently, the archaeological discovery of substantial numbers of Murex shells on Crete suggests that the Minoans may have pioneered the extraction of Imperial purple centuries before the Tyrians. Dating from colocated pottery suggests the dye may have been produced during the Middle Minoan period in the 20th–18th century BC.
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.
The true colour of Tyrian purple, like most high chroma pigments, cannot be accurately displayed on a computer display, nor are ancient reports entirely consistent, but these swatches give an indication of the likely range in which it appeared:
This is the sRGB colour #990024, intended for viewing on an output device with a gamma of 2.2. It is a representation of RHS colour code 66A , which has been equated to "Tyrian red" , a term which is often used as a synonym for Tyrian purple.