blue processed skins
(Rabbi Yehudah, Yerushalmi, Shabbath 2:3; Arukh s.v. Teynun; Koheleth Rabbah 1:9; Josephus 3:6:1, 3:6:4; Septuagint; Aquilla). Tachash in Hebrew. Others have 'black leather' (Saadia; Ibn Janach), that is, leather worked in such a manner as to come out dark and waterproof (Avraham ben HaRambam). In ancient Egyptian, tachash also denotes a kind of specially worked leather. See Ezekiel 16:10.
Other sources identify tachash as a species of animal. Some say that it is the ermine (Rabbi Nechemia, Yerushalmi, loc. cit.; Arukh, s.v. glaksinon. The word galy axeinon denotes the ermine, a member of the weasel family imported by the Axenoi (see Jastrow). Others state that it is a member of the badger family (Rashi on Ezekiel 16:10).
Others say that it is a colorful one-horned animal known as a keresh (Yerushalmi, loc. cit., Shabbath 28b; Tanchuma 6; Rashi; cf. Chullin 59b). Some say that this is a species of wild ram (Ralbag), possibly an antelope, okape or giraffe. Some see the one-horned creature as the narwhal (Mondon monoceros) which has its left tooth developed into a single long horn-like appendage. This animal, which can grow to be over 16 feet long, is occasionally found on the southern Sinai shores.
In Arabic, tukhush denotes the sea cow or dugong (Dugong hempirchi) an aquatic mammal which is found on the shores of the Sinai. Some thus say that the tachash is a type of seal, since its skins were used for the tabernacle's roof, and sealskins were often used for this purpose (cf. Pliny 2:56).