What is the difference between the Radzin techelet and the Efrat techelet (from the Murex snail)? Of course, the price is one. Nevertheless, I could not find something on your site to help me decide which to use. Some years ago, I had tied the Radzin techelet to my tallit gadol and, as time has passed, I'm now looking to replace my tallit and so am revisiting the subject. Your assistance is much appreciated.
Radzyn tekhelet is made using the ink from a cuttlefish (Sepia officinalis). R. Herzog, who corresponded with the Radzyner Rebbi about tekhelet, obtained the Rebbi’s formula directly from the Rebbi. He gave it to chemists for analysis and they told him that it was simply the formula for the well known synthetic dye “Prussian Blue”. They explained that the blue coloration comes from added metal filings, the cuttlefish ink being completely burned off and only supplying Nitrogen which could be obtained from a multitude of other organic sources such as Ox blood. As such, the Rebbi had apparently been duped by the chemists of his day because he writes explicitly that the color of the dye comes from the hillazon itself: “And with the help God it has come to my hands to extract, from the blood of the cuttlefish which is] black as ink, the color tekhelet in a manner which nothing affects the color other than the blood of the hillazon; and the chemical additives are colorless and only work to extract the color from the blood” (Sifrei HaTekhelet, Ptil Tekhelet, p.168). Another important point is the color itself. The Gemara (Baba Metzia 61) teaches that tekhelet is identical in color to the forgery dye “kela ilan” – known as “indigo” (used in the past for many things, such as Levis jeans). The Radzyn dye is not even close to resembling this blue, whereas the dye from the Murex trunculus (what you refer to as “Efrat techelet”) has been found not only to resemble it visually, but is molecularly identical to indigo! It should be noted that none of this is to impugn the good name of the Rebbi; on the contrary, he was undoubtedly the father of the tekhelet renaissance. He did much important work and investigation on a great many aspects of this issue which we still refer to today. And more importantly, he awakened in Am Yisrael the possibility of renewing this lost mitzvah d’oraita – not to speak of the awareness to work for the rebuilding of the Beit Hamikdash – she’yehiyeh bimheira b’yameinu. – Mois Navon.