Ruling 189. If the essence of an impure object changes in such a way that it transforms into a pure object, it becomes pure. For example, if impure wood burns and transforms into ash, or a dog falls into a salt marsh and transforms into salt [the ash and the salt are pure]. However, if the essence of the object does not change – for example, impure wheat is turned into flour or made into bread – then it does not become pure.

Ruling 190. A clay pitcher or something similar made from impure clay is impure. As for charcoal made from impure wood, in the event that none of the former physical properties is in it, it is pure. If impure clay is changed by fire into crockery or bricks, then based on obligatory precaution, it remains impure.

Ruling 191. An impure object about which it is not known whether it has undergone a transformation is impure.