Both the stones of the ramp and the stones for the altar [came] from the valley of Beit Kerem. They would dig below [the stones] virgin soil and would bring complete stones that were never touched by iron, because iron renders them [the stones] unfit by just touch. [They are also unfit] if they are chipped through any means. If one of them were chipped, it is rendered unfit, but the rest [of the sones] are not. The [walls and the the top of the altar] were whitewashed twice a year, once on Pesach and once on Sukkot. The vestibule [was whitewashed] once a year, on Pesach. Rebbi says, every Friday they would be whitewashed with a cloth because of the blood stains. The whitewash was not applied with an iron trowel, out of the concern that the iron trowel would touch the stones, and render them unfit, since iron was created to shorten man's days, and the altar was created to extend man's days, and it is improper that that the shortner be placed upon that which extender.
Sefer HaChinukh
The laws of the commandment - for example, from where they would bring these stones with which they would build the altar, that they, may their memory be blessed, said (Mishnah Middot 3:4) that they would bring them from virgin ground or from the Great Sea; the law of if metal touched a stone after the altar was built, whether all of it is disqualified or only it alone is disqualified; that which they, may their memory be blessed, said (Mishnah Middot 3:4), [that] when they whitewashed the altar twice a year, that they did not whitewash it with a tool that had iron in it, so that the iron not touch a stone; and the rest of its details - are [all] elucidated in Tractate Middot (See Mishneh Torah, Laws of The Chosen Temple 1).
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Sefer HaChinukh
And the matter of tsaraat is that one or more places on the skin of the flesh of a man become white - and these places be very white until their white resembles the white of the membrane of an egg and more than it in its whiteness. But the whole time that it is less dark in its appearance than the membrane of an egg, it is not tsaraat but rather a shiny spot (bohak) - meaning to say, a different illness that is not a type of tsaraat at all, but rather like types of rash and other types of [skin] ailments that occur with a person. There are four appearances to the tsaraat on the skin of a man's flesh: Two are primary sources (avot) - and they are the se'et and the baheret - and two are their derivatives. And that is [the meaning] of their, may their memory be blessed, saying (Mishnah Negaim 1:1), "The appearances of ailments are two which are four: Baheret [...] and its adjunct; se'et [...] and its adjunct." And the understanding of its adjunct is meaning to say, its derivative; as the expression, adjunct (sapachat) is only an expression of [being] secondary. And the Sages likened these four appearances: one to clean white wool, and that is the se'et; one to snow, and that is the baheret; one to the lime of the sanctuary, and that is the derivative of the baheret; and one to the membrane of an egg, and that is the derivative of the se'et (Mishnah Negaim 1:1). These are the impure ones and they combine, one with the other, to render impure (Mishnah Negaim 1:3). And anyone who does not recognize them through their differences and their names should only determine them by the mouth of someone who recognizes [them] (Shevuot 6a) - and as it is stated below in the laws of the commandment.
