longarekel– We (or at least I) am reffering to the Murex techeiles which is used by the zilbermans and Rav Shachter and basically anybody who wears techeiles and is not chassidish.
The Radzyner was proven wrong by Rav Yitzchag Isaac Haleivi Herzog after a chemical test revealed that the dye was Prussian Blue and had very little to do with the fish. The only difference between that and Prussian Blue was the source of Nitrogen which in prussian blue it came from a horse’s blood. Therefore it would make no sense to make a gezeira on kla ilan if you could use anything else. Thre were many other problems as well such as that the medrash is clear that there is a shell and that the dye binds very strong -neither of them being fulfilled with the radzyner Sepia.
Rav Herzog suggested that it could be the Murex just he had a few problems. 1- The shell was not the color of the sea as the gemara seems to say (acc. to rashi in menachos 44a) 2. the color extracted from the snail was purple not blue. 3. The dye did not stick strongly. So because of this He suggested another fish called the Janthina (which has many other problems such as that you cannot use it to dye and it is missing a lot of the ikar simanim)
Some 20 years ago it was discovered the answer to all of rav herzogs problems. 1- the shell IS the color of the sea when you take it out of the water and for the next few hours. After a while it looses that color and turns white we must assume that he only saw a snail that was out of the water for a while.
2- It was discovered if you keep it in the sunlight the dye turns blue and not purple.
3- The mitzious is that the scientists all agree that The murex is from the fastest dyes out there. However when dyed on a non wool material that it it does not bind very well at all, like described by the Sefer Hachinuch in 386 ??? ????? ?? ??? [????] ??? ????? ????? ??? ????
Besides for all this there are many rayos to the Murex including That the Chavos ya’ir in Mekor Chaim siman 18:3 and the Yaavetz In Mitpechehes Seforim 4 clearly say that the techeiles was made from the Purpura (the greek word for the Murex)