Notes on Tekheleth
I recently listened to a lecture by Rabbi Reisman, available here and on YUTorah.org, and rabbi Lebowitz’s response. I believe that Rabbi Lebowitz did a good job, but I would add:
1. I believe Rabbi Reisman is mistaken with regard to the meaning of the Talmudic Passage from M’nahoth 42b, which discusses testing, not tasting, the tekheleth dye once it is prepared. The confusion lies in the fact that in Mishnaic Hebrew, the verb t’ima is used, and it normally means a taste. As can be seen from Maimonides’ formulation in the second chapter of the laws of Tzitzith, it means to test the brew by dipping white wool strings into it. In this case, tasting is merely a borrowed term. (As a humorous aside, perhaps this has to do with phenomenon that in certain dialects of Hebrew, no distinction is made between the long A sound and the short E sound. ְטֵסְט and טֶסְט would therefore be homophones.)
2. I would refine Rabbi Lebowitz’s answer: Indeed, the Torah commanded us to use genuine tekheleth, and up until Mishnaic times, indigo, which is named for India, was not at all common in the land of Israel or Babylonia. Thus, even if the upper-classes may have already started to use indigo as the source for their coveted blue wool dye, real, snail tekheleth remained in demand, at least among Jews, because that is what the Torah demanded of them. Further, even among gentiles, real tekheleth was still a mark of status because, as Rabbi Herzog first pointed out, it was the cousin of the argaman, the expensive Tyrian purple, which also came from the murex and which could not be imitated by a vegetable dye.
From Rabbi Avi Grossman, here.