http://en.wikipedia.org/wiki/Tyrian_purple and http://en.wikipedia.org/wiki/Iles_Purpuraires show that blue dye was produced from the murex in ancient times in these locations. But on Ptil Tekhelet's website (tekhelet.com), they seem to admit that there is no clear historical evidence that anything but purple was produced from the murex in ancient times, and that any reference to purple snail dye in ancient writings refers to blue as well because blue is a shade of purple. Is there or is there not historical evidence that blue dye from the murex was produced in ancient times?

  • tekhelet.com/murbaat seems to say that they actually found fabric died blue so it appears that they also have "historical evidence". The Association of Orthodox Jewish Scientists had an article showing that exposure to strong light caused a boron bond breakage that made it blue and the double bond caused purple. This is only "evidence. "Proof" would require going back and observing the production of techelet and returning with samples. (:-) May 22, 2014 at 17:19
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    Even if blue dye was historically made from the murex snail in areas adjacent to the Mediterranean, that doesn't tell you that that dye was t'cheiles.
    – Fred
    May 22, 2014 at 18:01
  • @Fred, true, but that wasn't the question.
    – msh210
    May 22, 2014 at 19:03
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    @msh210 Then perhaps this should be migrated to History.SE?
    – Fred
    May 22, 2014 at 19:04
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    @Fred, the point of this question is to learn a point of history that's both [potentially] about the history of Jewish practice and [potentially] relevant to contemporary practice. It's reasonable to assume that a population of experts on Judaism would be more likely to be able to provide an expert answer to this question than the general population. As such, it's on-topic here whether it's also on-topic at History.SE or not. There'd be nothing wrong with posting a parallel question there to see what their history experts come up with, but I think migration, like closing, is unnecessary.
    – Isaac Moses
    May 23, 2014 at 17:49

2 Answers 2


A host of information about this topic can be found by browsing more of the Psil Tekhelet website, tekhelet.com. A presentation of a blue murex-dyed textile can be found here. There is much more information to be seen, and it cannot all be written in this forum. As far as I know, no actual tzitzis with blue threads of any kind have been discovered. However, Murex or not, the Gemara in Menachos gives detailed descriptions of the techeles dying process, which most authorities maintain was a blue-indigo dye. Indigo, called "kala ilan" in the Gemara, was also widely used.
It should be kept in mind that most Rabbinic authorities have not (yet?) accepted the Murex dye as legitimate techies.

  • Most of this post doesn't address the question at all.
    – Double AA
    May 23, 2014 at 20:23

We know that techelet was a blue dye, that murex was used then, and it best meets the description of techelet, and [here's the last bit that eluded Chief Rabbi Herczog] if you expose murex extract to UV light, it turns blue. So it's a very logical conclusion, though not airtight.

Similarly the Talmud says that a cheapskate could use indigo rather than techelet, and only God would know the difference. Murex blue is chemically identical to indigo. Again, airtight proof? No. But it seems to fit.

  • How does this answer the question?
    – Double AA
    May 25, 2014 at 1:41

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