Kelim, Chapter Five, Mishnah Nine
1) An oven which came cut up in sections from the craftsman’s house and he made for it hoops and put them on it, it is clean.
2) If it contracts impurity, and then he removed its hoops it is clean.
3) If he put them back on, it is still clean.
4) If he plastered it with clay, it becomes susceptible to impurity and there is no need to heat it since it was once heated.
Section one: The oven came to the person who ordered it cut up in pieces from top to bottom. The craftsmen had made hoops for it so that it could be held together while it was plastered and heated. The oven is still clean while he assembles it with the hoops because it is not yet ready to be used.
Section two: If he put a clay coating on it while the hoops were still attached and heated it up and then it became impure and then he removed the hoops, it is clean again because removal of the hoops causes the clay to fall off.
Section three: It is still pure when he puts the hoops back on because there is still no coating of clay.
Section four: If he again plasters it with clay, it is susceptible to impurity. It does not need to be reheated because it was heated up earlier while the hoops were still attached.