thank you. question from weekly Parsha. what was Tahashi and sinet ( purple) cover material and how they were made? why there were selected as special coverings?

ב"ה Shalom The Tachash is already mentioned in Shmot 25:5 and elsewhere in Shemot. Rashi there, says that it was a multicolored animal that existed only at that time. (see also Talmud Shabbat 28a). In regard to the purple, I assume you are referring to the "argaman". However, some understand "argaman" as a dark red. (see Ibn Ezra and Rambam on Misnha Kila'im 9:1.) In the Septuagint, "argaman" is translated as ""porphura" which means purple. That is how "argaman" is used in modern Hebrew. According to some sources it was extracted from lac, according to the Talmud (Yerushalmi Kila'im 9:1., it was derived from a living creature and according to others it was from an aquatic creature. (See Living torah to Shemot 25:5.) All the best