In the Artscroll Chumash Bamidbar 15:38, Tekhelet is translated as "turquoise wool". Does anyone have information on how 'wool' is derived from the word 'Tekhelet' or from the verse in which it is found? Thanks.
Tekhelet refers to a specific dyed textile prized in the ancient world. Traditionally and according to contemporary archeological understanding, the textile comprised wool dyed a blueish color with a specific sea creature, possibly identified with the hexaplex trunculus (or a subspecies thereof). (While very specific, that is the accepted meaning of the word, just as zahav refers to a specific metal - gold.)
ותנא דבי רבי ישמעאל כל בגדים צמר ופשתים הם ואמר רחמנא עביד ליה תכלת ותכלת עמרא הוא וממאי דתכלת עמרא הוא מדשש כיתנא תכלת עמרא הוא
a Tanna of the School of R. Ishmael [taught]: Wherever ‘garment’ [is written] such as is made of wool or flax [is meant], and yet the All Merciful said that in them ‘purple’ shall be inserted, and purple, surely, is wool. And whence is it deduced that purple is wool? Since linen34 is flax, purple must be wool.35
As the footnotes explain (essentially Rashi’s explanation):
(34) In the description of the materials of the High Priests’ garments (Ex. XXXIX, 1ff).
(35) As the garments were either of wool or flax, and linen (flax) was specified in the case of one, all the others must have been wool.
In actuality, the term (in this pasuk) refers to any thread which is to be dyed. However, the normal usage of the term (without the kind of fabric being dyed) means wool as in the construction of the mishkan and the priestly clothing.
Rav Hirsch explains on Beha'aloscha 15:38
דַּבֵּר אֶל בְּנֵי יִשְׂרָאֵל וְאָמַרְתָּ אֲלֵהֶם וְעָשׂוּ לָהֶם צִיצִת עַל כַּנְפֵי בִגְדֵיהֶם לְדֹרֹתָם וְנָתְנוּ עַל צִיצִת הַכָּנָף פְּתִיל תְּכֵלֶת:
פְּתִיל תְּכֵלֶת means a thread that is dyed with the color techeiles.
Rav Hirsch explains that the basic beged referenced in the Torah is wool or linen. However, the usage of the terms in Tetzaveh 28:5
וְהֵם יִקְחוּ אֶת הַזָּהָב וְאֶת הַתְּכֵלֶת וְאֶת הָאַרְגָּמָן וְאֶת תּוֹלַעַת הַשָּׁנִי וְאֶת הַשֵּׁשׁ
They shall take the gold, the blue, purple, and crimson wool, and the linen,
Shows that when the name of the dye alone is used, then it refers to the dyed wool, as opposed to the linen which is referred to separately.
We therefore, refer to the term techeiles as normally wool dyed with techeiles
בגדיהם We have repeatedly had occasion to remark -- at the בגדי כהונה -- that in the Torah wool and linen are taken as the real materials used for clothes, and hence by בגדים סתם as a rule only woolen or linen garments are to be understood.
Rav Hirsch also points out that the connection of Ki Teitzei 11-12 leads to the statement that tzitis made out of wool or linen are valid for garments made out of any material, but if made out of other materials are only valid for garments made out of the same material (see רשבא on Sab. 27b).