10 Unique Pigments That You Have Never Heard Of, Hannah Lane, for The Collector.

 Tyrian purple was reserved for royalty, it was made from the shells of two mollusks found only in the Mediterranean sea, Thais Haemastoma and Murex Brandaris. When their shells are cracked open there is a gland inside that when squeezed produces a single drop of clear fluid. When exposed to sunlight, this glandular fluid starts to change colour, from clear to pale yellow, then sea green, then blue, and finally, it becomes dark purple. Unfortunately for the mollusk harvesting this gland kills them.

Getting Tyrian purple was a difficult process one drop at a time, the potent smelling fluid was mixed in a barrel with urine and left to ferment for 10 days after which fabric was soaked in the barrel to absorb the colour.

History is full of references to Tyrian purple; Julius Caesar, gave his newborn son, Caesarion, a toga dyed in this color and it is mentioned in famous works like the Iliad and Aeneid.
Researchers believe it was used as early as the 15th century BCE.

Source:
10 Unique Pigments That You Have Never Heard Of, Hannah Lane, for The Collector.