Dick Petit encouraged me to contact André Verhecken, a chemist who is
interested in Tyrian purple. He responded quickly and here is his
contribution to the discussion on Conch-L.

Andrew K. Rindsberg
Geological Survey of Alabama

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Dear Dr Rindsberg,

It's nice to hear from other people interested in Tyrian purple !

Most of the questions you suggest have been treated in my paper "The indole
pigments of Mollusca", Annales de la Société royale zoologique de Belgique,
119 (2): 181-197  (1989).  [SNIP] There is also my "Experiences with
mollusc purple", La Conchiglia, 22 (250-252):32-34, 46. with color
illustrations of the formation of the purple dye.
So, in this context you will understand that I don't feel like repeating
myself.

As to you last question (imitations of purple): this has certainly been
done, already in Antiquity, with other natural dyes.  And early this
century, a synthetic dye was made before the structure of the mollusc
purple was known; and afterwards they turned out to be the same!  But the
synthetic dye never was a commercial success, because the color shade was
not good enough commercially.

As a matter of fact, there is a huge literature on Tyrian or mollusc
purple. The Austrian scholar published a 4-volume work on the subject: "Ein
Beitrag zur Purpurkunde", Mayer & Müller, Berlin (1898, 1906, 1908 and
1911).  It seems to be a rare work, perhaps it is only in a central library
in the US.

If you have other questions regarding purple, please don't hesitate to
contact me.

Sincerely,

André Verhecken