Four exciting breakthroughs in our understanding of tekhelet have been reported recently:
The main dyestuff of tekhelet dye has now been discovered. The main and characteristic ingredient of tekhelet is a hitherto unknown dyestuff named 6-monobromo-indigotin (MBI), in admixture with the two previously-known ingredients, 6,6′-dibromo-indigotin (DBI) and indigotin. Currently, we have been investigating the unique chemistry of MBI, which – when heated to 60 degrees C – changes irreversibly from its initial violet colour to blue, without any alteration in its chemical structure and composition. The DBI ingredient is also the dyestuff of Tyrian purple (Hebrew argaman,ארגמן), that is the dye produced from all other species of dye-shellfish, except banded dye-murex used for making tekhelet. The indigotin ingredient is a blue, that is also the vegetable dyes woad and indigo (קלא אילן).
The millennium-old mystery of how tekhelet was dyed has now been unraveled by Edmonds and Boesken-Kanold . It is a unique bacterial fermentation taking a week, that converts the dye to a soluble form, which readily dyes wool to tekhelet. This natural process is spontaneous; and it has been restored to work in practice.
Variations in the dye colour obtained with different specimens of banded dye-murex are now attributed to the size (i.e. the age) of the snail. The younger individuals largely give blues, while the older ones mostly give purples. Accordingly, use smaller shellfish to get a tekhelet colour!
Excavations of High Priestly residences in Temple-era Old-City Jerusalem , have uncovered intact shells of banded dye-murex . This finding indicates that the shells were treasured as prestigious objects. Perhaps these shells were prized as revered symbols of the sacred goods made from them.
But not only for tekhelet! Also the opercula ציפורן of this shellfish were evidently used to make the onycha שחלת ingredient of the Holy Incense קטורת (Exod. 30: 34).