On new vessels. However, one does not recite the Shehecheyanu blessing on the mitzvah, since it does not occur from time to time. Nevertheless, this requires further examination, as in Yoreh De'ah section 28, it is written in the gloss that one recites Shehecheyanu on covering [blood], and in section 265, paragraph 7, it states that one recites Shehecheyanu for circumcision and the redemption of the firstborn. It must be said that those cases are not as common. See Siftei Kohen (Shakh), who wrote something similar to this. However, there is a difficulty, for on new vessels one must recite the blessing at the time of acquisition, as stated in Orach Chaim section 223, paragraph 4. So why does it say [that one recites the blessing] when one makes tzitzit on it? It must be that the case discussed is one where the blessing was not recited at the time of acquisition. Alternatively, the distinction is that one only recites Shehecheyanu when purchasing a garment that is immediately ready to wear. But if one buys fabric and makes it into clothing, then the blessing is recited at the time of wearing, as stated in Orach Chaim section 600, paragraph 2. Here, since one is making tzitzit on it, the blessing is recited incidentally at the time of performing the mitzvah.