Parshas Terumah marks the beginning of the most-discussed topic in the Torah: the building of the Mishkan, its vessels, and the kohanim’s garments.
Rabbeinu Bechaya (25:3) points out that we do not find silk among the materials donated to the building of the Mishkan. He explains that this is because silk comes from worms and the Gemara (Shabbos 28a) says that only materials from tahor items were used in the Mishkan.
One obvious question: Many of the items were dyed in tola’as shani – a red color dye. But since tola’as is a worm, how could this dye have been used in the Mishkan? I have seen an answer to this question which explains that the dye does not come from the actual worm; it comes, rather, from grain the worm is in.
Another question concerns the blue dye called techeiles. Techeiles comes from a non-kosher worm – the chilazon – yet it was used in the Mishkan. How can this be?
The truth is there is a dispute as to the kashrus of the chilazon. Rashi (commenting on Sanhedrin 91) says that the chilazon was a worm from the sea, implying that it was not kosher. But the Radziner Rebbe, in Pesil Techeiles, writes that the Chida maintains that the chilazon was a kosher fish. The Rambam (Hilchos Tzitzis 2:2) writes that the chilazon was a fish, and the Noda B’Yehudah writes explicitly that the Rambam maintains that the chilazon was a kosher fish. According to this view, it is understandable how the blood of the chilazon could have been used in the Mishkan. According to Rashi, though, the question still remains.
The Radziner Rebbe cites several Rishonim who maintain that one may eat the blood of a non-kosher fish. Only the flesh of the fish is prohibited to consume; the blood is permitted mi’de’oraisa. Since the techeiles dye is produced from the blood of the chilazon fish, it is understandable how it could have been used in the Mishkan, even according to Rashi.
The Chasam Sofer addresses this topic in his teshuvos (Orach Chayim 39) in regards to items in shuls. The Darkei Moshe (Orach Chayim 153) writes that a shul, like the Mishkan, must only be built from tahor material. Why, then, wonders the Chasam Sofer, do so many shuls use silk in constructing their items of kedushah?
One could suggest that we distinguish tamei animals from the items they produce. The only problem is that Rabbeinu Bechaya states explicitly that products from non-tahor items – not just the non-tahor items themselves – were also unfit for use in the Mishkan.
The Chasam Sofer writes that the Ran is unsure whether we rule in accordance with the abovementioned Gemara that states that only kosher items may be used in building the Mishkan. He also suggests that other Rishonim may disagree with Rabbeinu Bechaya and opine that something formed from non-kosher material – e.g., dye or silk – looses its non-kosher status, and may be used in the Mishkan or a shul. According to this view, the Gemara which says they may not be used is referring only to hides, which, unlike silk or dye, do not undergo any radical transformation.
The Noda B’Yehudah (Tenina Orach Chaim 3) writes that dyes in the Mishkan were allowed to come from forbidden material. Therefore, the blood of the eilim was permitted to be used as a dye. Similarly, the blood of the chilazon was permitted to be used for techeiles even according to Rashi who maintains the chilazon was not kosher.