Royal Purple (also called Tyrian Purple or Byzantine Purple) is the deep purple pigment used for elite clothing beginning in the Roman period and illuminated manuscripts through the Middle Ages. The dye comes from several species of the carnivorous marine mollusc, the whelk (including but not limited to Murex spp, Nucella spp and Purpura spp).
Whelks which produce purple dyes are found world-wide, including the Americas, but Royal Purple was most famously first produced in or near the city of Tyre in Lebanon, during the Imperial Roman period.
The purple-bearing part of the whelk is the hypobranchial gland, which produces a colorless or yellow mucus. When exposed to sunlight and air the mucus changes color several times, but at last becomes a stable, non-water-soluble purple pigment somewhere between blue-violet and red-purple. While the pigment itself is created without additional manipulation, to make the quantities of dye required for the elite purple purposes, a vat-dying process was invented.
History and Royal Purple
According to historical documents (specifically, Book 8 of Pliny the Elder’s Historia naturalis), processing of whelk mucus involved adding honey or salt, water, and long-term heat processing in a lead vessel.
Archaeological sites with evidence for whelk dying include a 7th century AD dye workshop on the island of Inishkea North in County Mayo, Ireland, excavated in the 1950s by Françoise Henry. Inishkea North was home to an early Christian monastery, where the monks were known to have produced whelk dyes.
Carole Biggam's article listed below is a comprehensive history of whelk dying, including linguistic and historical data.
Biggam, C. P. 2006 Knowledge of whelk dyes and pigments in Anglo-Saxon England. Anglo-Saxon England 3523-55.
This glossary entry is part of the Dictionary of Archaeology.