Tyrian purple


Variously known as Royal purple, Tyrian purple, purple of the ancients, this ancient dyestuff, mentioned in texts dating about 1600 BC, was produced from the mucus of the hypobranchial gland of various species of marine molluscs, notably Murex. Although originating in Tyre (hence the name), man's first large scale chemical industry spread throughout the world. With the decline of the Roman Empire, the use of the dye also declined and large scale production ceased with the fall of Constantinople in 1453 (29 May, actually). It was replaced by other cheaper dyes like lichen purple and madder.

The ancient process was described by Pliny in the mid first century AD ...

Murex trunculus

Murex brandaris

Two kinds of shell-fish furnish the purple and the conchylian dyes - the colours used for both are the same, but they are mixed indifferent proportions....

Purples are caught with a sort of small wicker basket cast into the deep, and containing as bait bivalves which snap their shells together, as mussels are known to do. These bivalves, though half-dead, revive on returning to the sea and gape open greedily. The purples seek them out and attack them with protruding tongue, but the mussels shut up as soon as they feel the sting, and hold their assailants fast. Thus suspended, the purples are taken up, caught by their own greed.

The best time to catch them is after the rising of the dog-star or before spring arrives, for, when they have produced the honeycomb-like exudation, the juice is too thin. Yet, this fact, although of the utmost importance, is not recognised in the dye factories. The vein already mentioned is then extracted and about a sextarius [ca. 7 lb] of salt added to each hundred pounds of material. It should be soaked for three days, for the fresher the extract, the more powerful the dye, then boiled in a leaden vessel. Next, five hundred pounds of dye-stuff, diluted with an amphora [about 8 gallons] of water, are subjected to an even and moderate heat by placing the vessels in a flue communicating with a distant furnace.

Meanwhile, the flesh which necessarily adheres to the veins is skimmed off and a test is made about the tenth day by steeping a well-washed fleece in the liquefied contents of one of the vessels. The liquid is then heated till the colour answers to expectations. A frankly red colour is inferior to one with a tinge of black. The wool drinks in the dye for five hours and after carding is dipped again and again until all the colour is absorbed.

William Cole in 1685 described in some detail how to use Nucella lapillus (his drawing on the left) to obtain the purple dye.

Nucella lapillus he "found this species on the shores of the Bristol Channel, which on cracking and picking off the shell, exhibited a white vein lying transversely in a little furrow or cleft next the head of the fish; which must be digged out with the stiff point of a horse hair pencil being made short and tapering; which must be so formed by reason of the viscous claminess of that white liquor in the vein so that by its stiffness it may drive in the matter into the fine linnen or white silk ....... if placed in the Sun will change into the following colours, i.e., if in the winter about noon, if in the summer an hour or two after sunrise and so much before setting (for in the heat of the day the colours will come on so fast, that the succession of each colour will scarce be distinguishable) next to the first light green will appear a deep green; and in a few minutes this will change into a dull sea green; after which, in a few minutes more, it will alter into a watchet blue; from that in a little time more it will be purplish red; after which, lying an hour or two (supposing the Sun still shining) it will be of a very deep purple red; beyond which the Sun can do no more."

The major component of the dye is 6,6'-dibromoindigo. Paul Friedländer was the first to determine the composition of the dye from Murex brandaris in 1909. Here is his recipe.

Für die Isolierung und Reindarstellung des Farbstoffs benutzte ich mit kleinen Modifikationen das schon früher (l. c.) angegebene Verfahren. Die herauspräparierten Drüsen wurden auf Filtrierpapier gestrichen und der Farbstoff durch kurzes Belichten in der Sonne entwickelt. Hierauf maceriert man das Papier durch halbstündiges Erwärmen auf dem Wasserbade mit mäßig verdünnter Schwefelsäure (1:2), wäscht den Brei wiederholt mit heißem Wasser auf der Nutsche aus und extrahiert ihn zur Entfernung von Verunreinigungen im Soxhlet mit Alkohol. Zum Extrahieren des Farbstoffs selbst eignet sich Benzoesäureäthyläther, aus welchem er sich in flimmernden, kupfer-glänzenden Krystä1lchen ausscheidet. Zur völligen Reinigung wird nochmals aus Benzoeäther; schließlich aus Chinolin umkrystallisiert (wegen der Schwerlöslichkeit durch Extraktion aus einer Soxhlet-Hulse, die in einen Kolben unterhalb des Kühlrohrs aufgehängt wird).

Die Ausbeute an reinein Farbstoff betrug 1.4 g aus ca. 12000 Schnecken.

P. Friedländer: Über den Farbstoff des antiken Purpurs aus murex brandaris.
Berichte der Deutschen Chemischen Gesellschaft, 1909, 42, 765-770

The chemical synthesis of 6,6'-dibromoindigo was first reported in 1903 by Sachs and Kempf. A recent variation can be found

How the mollusc does it can be found

Much more about the chemical synthesis can be found
The most unusual aspect of Tyrian purple is the colour. In solution, the colour is blue but as a dye in the solid state it is purple. Details of the spectroscopy can be found
Look here for a picture of the X-ray crystal structure of 6,6'-dibromoindigo. The parallel rings are closer together here than in indigo because of van der Waals interaction of the bromine atoms, leading to the purple colour in the solid state.
For further reading about Tyrian purple, see this up-to-date bibliography

Look here for more info about tekhelet...
for example, from Tekhelet by Baruch Sterman

"In 1985, Rabbi Eliahu Tevger of Jerusalem began researching a book on the subject of tsitsit. He became convinced that the true tekhelet - from the trunculus - had been discovered. He was determined to actualize his newfound knowledge and, after much trial and error, Tevger succeeded in applying the process according to the details of halakha from beginning to end. A few years later, Joel Guberman, Ari Greenspan and myself joined with Rabbi Tevger in an effort to provide tekhelet to the general public." ...
"At present, more than 2,500 Jews from various communities the world over are wearing tekhelet obtained from the true hillazon, the Murex trunculus. After a 1,300 year interlude, Jews from Jerusalem to New Jersey are once again wearing the royal, priestly garb with the cord of tekhelet, as commanded in the Bible."
and lots of other information, including a bibliography.

Tyrian purple is not just a dye. Have a look at Inge Bösken-Kanold's page with paintings using mollusc pigments in France.

For blue-dyed material from the mollusc ask here for more info about tekhelet.

The pigment is available from Kremer pigments

Or contact Peter Imming.

Mexican purple
Purpura pansa
Photo by Eric Mindling
More here
They do things differently in Mexico with Purpura pansa. Squier describes the process in Nicaragua in 1852 ...

The process of dyeing the thread illustrates the patient assiduity of the Indians. It is taken to the seaside, when a sufficient number of shells are collected, which being dried from the sea water, the work is commenced. Each shell is taken up singly, and a slight pressure upon the valve which closes its mouth forces out a few drops of the colouring fluid, which is then almost destitute of colour. In this each thread is dipped singly, and after absorbing enough of the precious liquid, is carefully drawn out between the thumb and finger, and laid aside to dry. Whole days and nights are spent in this tedious process, until the work is completed. At first the thread is of a dull blue colour, but upon exposure to the atmosphere acquires the desired tint. The fish is not destroyed by the operation, but is returned to the sea, where it lays in a new stock of colouring matter for a future occasion.

Some places to look
Oaxaca Natural Dye

Carthaginian purple
Pictures of how it is done in Tunisia

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