Biblical blue

Spanier E. (ed.) (1987), The Royal Purple and The Biblical Blue Argaman and Tekhelet, Keter, Jerusalem. 

Indigo is a vat dye, which means that it was once applied in special vats. It and other vat dyes are insoluble in water. In dyeing, indigo is converted, or reduced, to a white form, which is soluble. Yarn or fabric is then dipped in the vat containing the reduced dye, which on leaving the vat is oxidized in the air back to blue. Tyrian purple and biblical blue are also vat dyes. 

The historic interest in this dye is evidenced by the fact that Pliny the Elder (A.D. 23-79) devotes six chapters of his celebrated Natural History to its production, including treatises on the nature and kinds of shellfish, the history of its appearance in Roman outerwear, the high cost of the dye, and the methods used to obtain and process it (7). Furthermore, volumes, and indeed, doctoral dissertations have been written on its role in the production of the Biblical blue, or tekhelet, but the nature of this mysterious blue remains doubtful to this day (5). 

The Royal Purple and the Biblical Blue Spanier, E., Ed. Keter Publishing House ... 

Koren ZC (2011) Tekhelet announcing the discovery of the first authentic biblical-blue tekhelet from ancient Israel after a millennium and a half of disappearance. Presentation at the International Edelstein Color Symposium, Shenkar College of Engineering and Design. Ramat-Gan, Israel, 27-28... 

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