Tyrian Purple
This excerpt is from my current reading, an excellent book by Philip Ball called Bright Earth (citation below). This bit struck me for two reasons: for filling in details about Tyrian purple (i.e., Roman Imperial Purple) and its manufacture, plus the sense it provides that the rich and powerful have always gone to considerable lengths with ridiculously visible consumption.
The manufacture of Tyrian purple was known in Asia Minor since the fifteenth century B.C. The Greeks learned the art from the Phoenicians; garments dyed with Tyrian purple are mentioned in Homer's Illiad and Virgil's Aeneid. The dye is extracted from two species of shellfish, known in Latin as the buccinum (Thais haemastroma) and the purpura (Murex brandaris), native to the Mediterranean Sea. According to George Field, Greek legend has it that Tyrian purple was discovered by Hercules, who, seeing the purple-stained mouth of his dog, attributed it to the shellfish the dog had just eaten. Others say the dog's master was the Phoenician god Melkarth.
The colorants are produced in a gland called the "flower" or "bloom," near the head of the mollusk, which contains a clear fluid. This liquid was extracted either by breaking open the shells or by squeezing them in a press. on exposure to sunlight and air, the fluid becomes transformed from a whitish color to pale yellow, green, blue, and finally purple. It is hard to imagine that the alchemical significance of this sequence would not have excited great interest.
Aristotle describes the extraction process in his Historia animalium: "The 'bloom' of the animal is situated between the quasi-liver and the neck, and the co-attachment of these is an intimate one. In color it looks like a white membrane, and this is what people extract; and if it be removed and squeezed it stains your hands with the color of the bloom . . . Small specimens they break in pieces, shells and all, for it is no easy matter to extract the organ; but in dealing with the larger ones they first strip off the shell and then abstract the bloom."
Each shellfish yielded just a drop of the dye, which was why the stuff was so fiendishly precious and why a significant proportion of the Phoenician population was employed in its manufacture. One ounce of the dye required the sacrifice of around 250,000 shellfish. The shell piles of the Phoenicians still litter the eastern shore of the Mediterranean.
[…]
But the centuries-old method of preparing the purple was lost to the Western world when Constantinople fell to the Turks in 1453. Despite the accounts of the classical scholars, the process remained a mystery for centuries thereafter until a French zoologist named Félix Henri de Lacaze-Duthiers rediscovered it in 1856 — an auspicious year for purple, as it turned out [referring to William Perkin's discovery of the dye mauve that year]. The Frenchman saw a Mediterranean fisherman mark his shirt with a yellow design using a Thais shellfish; the design subsequently turned purple-red in the sun. It was not until `909, however, that the Austrian chemist P. Friedlander deduced the full chemical nature of the colorant molecure and discovered that it was almost identical to blue indigo.Who would suspect that a pea plant native to India should have anything to do with shellfish in the Mediterranean? Yet the organic compound responsible for the Imperial purpura differs from the blue extract of the Indigofera plant only to the extent of having a couple of bromine atoms where hydrogens sit in indigo. Why shellfish should produce such a close variant (chemists would say derivative) of a complex substance found in a plant is not at all clear.
[from Philip Ball, Bright Earth: Art and the Invention of Color, New York: Farrar, Straus and Giroux, 2001, pp. 199–201.]
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on Friday, 12 January 2007 at 20.40
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ah yes — something guaranteed to engage moi, a chemist through and through. one of the interesting points about tyrian purple is it is one of the very few natural products that is a bromide — lots of chlorinated naturally sourced chemicals out thar, but not many at all that are brominated.
it's 6,6'-dibromoindigo. MY roots are not "of the purple", no upper-class romans for me; I'm more (just-plain-) indigo; not for its blue-jeans connections, but because my ancestors painted themselves [indigo] blue with woad while trying to scare off the military-class romans. didn't work, but wandering around wearing nothing but blue dye does have a certain cachet.
on Saturday, 13 January 2007 at 00.45
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I was hoping, Chris, that this bit of chemical lore might attract your attention. The author, Ball, did his degrees in chemistry, so my sense is that we're getting an accurate (and interesting) picture of all the chemistry behind color and pigments and their use and influence in art. I find it all terribly engaging.
That's a fascinating thing about the bromides; even more so that its name incorporates "indigo", deepening the connection. And why in the world should these shellfish mess with bromine?
It was near this discussion, by the way, that he also discussed your great-greats' use of woad, and the fact that using it as a dye sounds like a terribly complicated and dangerous affair likely to ruin the fabric. But, useful enough if you want to be a terrifyingly blue warrior en plein air I suppose.
on Monday, 15 January 2007 at 00.09
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ah well, dilettante chemist, that's moi.
the structure of indigo was worked out first (and it is the simpler molecule), and so it was very logical to refer to Tyrian purple as "dibromo indigo".
nearly all dyes are polycyclic aromatic compounds, where most of the atoms are in the same plane, and there are lots of (conjugated) unsaturated bonds. This makes for lots of low energy (that is, not very far above the ground-state) pi* (antibonding) orbitals. The energy difference between the ground-state (electron-occupied) pi orbitals on these molecules, and the (empty) pi* orbitals is in the visible part of the spectrum, so they absorb visible light with the greatest of alacrity. Some of them are natural-source, and these days the vast majority are synthetic.
there are those who say that any dye ruins the fabric, but shirley if you intend to turn the fabric blue, then the action of woad (aka indigo) is what you want.
I regularly have to remind my students when they're doing qualitative analysis, using Ag+ ions, that these ions will photoreduce really easily (the entire basis of the photographic film industry), and so wash if you spill silver solutions on yourself. If you see the skin starting to darken, it's too late. Ag+ reduces to finely divided Ag metal, which is black, and stains the skin protein permanently – it'll last until the skin replaces itself. That's 2-3 days on the palms, and 4-5 days on the backs, unless you scrub hard to exfoliate.
Now there are many synthetic dyes out thar now. I got to play with a number of them in microbiology labs, learning all about malachite green and carbol fuschin and the like. another one is crystal violet. Engineering students around here tend to use it as part of their orientation rituals in September, and here is some photographic evidence that I got in years gone by.
I made further comments on this in soc.motss (featuring jockstraps).
on Tuesday, 16 January 2007 at 11.27
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We had a gubernatorial candidate a few years back who had taken "sea silver"(?) for awhile, orally I presume. It had turned him a permanent grayish/bluish hue. I found this creepy and fascinating.