From R. Tucker Abbot's "The Kingdom of the Seashell:"

"...Although the dye was probably known to and used by Neolithic man, the
earliest evidence of its use points to the Mediterranean island of Crete at
least as early as 1600 B.C. Almost every shell collector who has collected
live Purpura or Nucella rock shells has noted that the mucous juices from the
snails stain the cloth collecting bags and fingers a deep magenta purple.
Early man could not have overlooked this fact....

The earliest authentic accounts of the preparation of the dye were given by
Aristotle and later by Pliny.  There were two species of Murex and one Thais
used in the Mediterranean by the Minoans and later by the Phoenicians, who
perfected the manufacture of the dye and maintained a monopoly for several
centuries from about 300 B.C. to A.D. 150.   Pliny's description is quite
accurate in view of what is known today....The liquid was obtained from a
transparent branching vessel (the hypobranchial gland on the roof of the
mantle) behind the neck of the animal.  At first the liquid was the color and
consistency of thick cream (it is a yellowish mucous fluid that, in the
presence of direct sunlight, gradually--in a matter of ten minutes--turns to
greenish, then bluish and finally purple red).  Small shells were crushed in
rock rnortars, while larger shells were broken with a cleaver, in order to
extract the entire soft parts.  The slimy bodies were steeped in salted water
for three days and then set to boil in vessels of tin or lead.  Skeins of
wool or cotton threads were continuously dipped into the fluid over a period
of five hours and later dried and carded.  Redipping produced darker shades.

Evidently the Phoenicians of Tyre and Sidon (no in Lebanon) used two
different dye baths, one made from the juices of Murex brandaris, the other
from Thais haemastoma.  Their dyed wool was very highly esteemed, and during
the reign of the Roman Augustus, a pound of dyed wool sold for 1,000 denarii,
a sum now roughly calculated to equal $150.  The dye itself was very costly,
since it took many thousands of hours to collect the shells, each of which
yields just a few drops.  For fifty pounds of wool, the ancients used no less
than 300 pounds of liquid dye.
The dye was very fast and did not fade for many years.  When Alexander the
Great took possession of Susa, he discovered among the treasures of Darius
over 5,000 pounds of purple cloth still bright and fresh after 180 years of
storage.  Some museums today possess mummy wrappings dyed with molluscan
purple that still show strong coloration after thousands of years....

sj