Leviticus 13:54

50 And the priest is to examine the mildew and isolate the contaminated fabric for seven days.

51 On the seventh day the priest shall reexamine it, and if the mildew has spread in the fabric, weave, knit, or leather, then regardless of how it is used, it is a harmful mildew; the article is unclean.

52 He is to burn the fabric, weave, or knit, whether the contaminated item is wool or linen or leather. Since the mildew is harmful, the article must be burned up.

53 But when the priest reexamines it, if the mildew has not spread in the fabric, weave, knit, or leather article,

54 the priest is to order the contaminated article to be washed and isolated for another seven days.

55 After it has been washed, the priest is to reexamine it, and if the mildewed article has not changed in appearance, it is unclean. Even though the mildew has not spread, you must burn it, whether the rot is on the front or back.

56 If the priest examines it and the mildew has faded after it has been washed, he must cut the contaminated section out of the fabric, leather, weave, or knit.

57 But if it reappears in the fabric, weave, or knit, or on any leather article, it is spreading. You must burn the contaminated article.

58 If the mildew disappears from the fabric, weave, or knit, or any leather article after washing, then it is to be washed again, and it will be clean.

Read all of Leviticus 13