Numbers 31:22

אך את הזהב וגו׳ ONLY THE GOLD etc. — Eleazar said: Although Moses has only admonished you concerning the laws of uncleanness caused by contact with a corpse, you must further be admonished concerning the laws of removing anything unclean that has been absorbed by vessels. The word אך is a restrictive term — it is as much as to say, “You are restricted from using vessels even after they have been cleansed from uncleanness caused by reason of a corpse until they shall have been cleansed also from what they have absorbed of that flesh which is forbidden as being that of an animal not killed in the proper manner.” And our Rabbis said that the words אך את הזהב are intended to intimate that it is necessary to remove its rust before he does the rite of removing the forbidden food that has been absorbed. This, they say, is the purpose of the term אך, — that there should be no rust there: Only (אך) the metal — it shall be as it should be (the metal without anything else, such as rust) (Yalkut Shimoni on Torah 785; Rabbenu Asher on Pesachim 30b states that this is to be found in Siphre, but it is missing in our editions of the work).

only the gold, and the silver, the brass, the iron, the tin, and the lead,

אַ֥ךְ אֶת־הַזָּהָ֖ב וְאֶת־הַכָּ֑סֶף אֶֽת־הַנְּחֹ֙שֶׁת֙ אֶת־הַבַּרְזֶ֔ל אֶֽת־הַבְּדִ֖יל וְאֶת־הָעֹפָֽרֶת׃