Leviticus 13:57-59

57If the spot later reappears on the clothing, the fabric, or the leather article, the mildew is clearly spreading, and the contaminated object must be burned up.

58But if the spot disappears from the clothing, the fabric, or the leather article after it has been washed, it must be washed again; then it will be ceremonially clean.

59“These are the instructions for dealing with mildew that contaminates woolen or linen clothing or fabric or anything made of leather. This is how the priest will determine whether these items are ceremonially clean or unclean.”