Shabbat 58: Cows' Bells and Ritual Purity

At the start of our Mishna, the rabbis consider whether slaves can wear seals on their on their clothing or around their necks on Shabbat while in the public domain.  Can a bell be hung around his neck? What if a bell is around his clothes?  Can cows go out with bells around their necks, or around their fabric around their necks?  And what is the issue here - ritual impurity?

On animals, theses are considered to be burdens rather than ornaments.  Seals and bells cannot become ritually impure because animal ornaments and utensils on animals do not become ritually impure.  

The Gemara speaks about who made the seal and the substance used to make it.  Does it matter if the seal is made of clay; if it is unimportant to the master who made it?  The rabbis debate their different positions: either seals cannot become ritually impure or they cannot.  The rabbis try to discern whether the baraita was referring to vessels of stone, dung, and earth or those of metal.  In the same baraita, were we taught that the problem with a bell is that it can become detached and then carried on Shabbat.  Bells woven into a garment are thus permitted.

The bell of a door is ritually pure.  The door is not a vessel, but part of a house, which is attached to the ground.  Anything attached to the ground maintains that status of ritual purity.  If a bell from a door is converted into a bell for an animal, its status can change.  When the bell now has an infal, a clapper, the bell can become ritually impure.  The clapper may change the bell into a vessel.  To become ritually pure again, it should be put through fire and then sprinkled with water.  If it cannot be put through fire, it should be put through water.