Tibetan bowls are made with the "seven sacred metals" of Tibet. They are made with prayers and chanting. The first time she heard one played, my mother, who knew nothing about Tibetan bowls or how they were made, said she could hear voices singing.
Originally I believe Tibetan bowls were orphaned offering bowls. That is, offering bowls come in sets of seven. Probably when one bowl was lost or broken, the whole set was replaced, and the orphaned bowls were used for meditation.
According to a Tibetan lama who used to teach a group that I belonged to, Tibetans only tap the bowls. They don't play them by rubbing a stick around the rim as we do.
The most important aspect of caring for Tibetan bowls is to treat them with respect. That means never set a bowl directly on the floor. It also means to treat them as sacred objects, not as toys.
Remember that the bowls will dent or break if dropped. Store them safely. Use a padded bag to carry them. Don't drop the bag or let it crash into things.
To me it's easier to play several bowls, along with some tengshas and bells, while sitting on the floor. So I keep my bowls wrapped in beautiful pieces of cloth that I spread out around me on the floor to set the bowls on.
Some of the decorative wooden strikers that come with Tibetan bowls these days are useless for playing. They are not shaped right for rubbing around the rim, and some are too rough.
Instead, you can use a plain wooden dowel at least an inch in diameter and about 8 to 10 inches long. I recommend buying a one-inch dowel and about a 1 1/4 or 1 1/2- inch dowel to use with different size bowls. You need the larger size for larger bowls, especially the thinner ones.
Dowels come in about 3-foot lengths. If you buy dowels at Home Depot or Lowe's, they will cut the dowels for you. Just be sure to sand the ends smooth. For striking the bowls (to get that lovely gong sound), you should lightly glue a strip of felt (about 1 1/2 inches wide) all the way around one end of each striker.
The leftover dowels can be cut into several sets of strikers. They make great claves, too. They are very inexpensive, and you can share them with friends.
Some of the best-sounding bowls appear to be new but made of the sacred metals. I suspect that they are made from old dented or broken bowls that have been melted down and reformed.
Some of the old bowls appear to have been made by hammering the metal into shape. The new bowls look to be turned on a lathe or otherwise shaped by some kind of rotary tool.
The lower the quality of the bowl, the more likely it is to tarnish. I suspect that a few of the bowls out there are not really made from all seven of the sacred metals--or maybe not quite in the right proportions. The sound does not resonate for as long as the sound of the good bowls.
You can polish them with brass and copper cleaner. To keep bowls from tarnishing (if you care about that), try covering them with a very thin layer of paste wax as people do to keep silver pieces from tarnishing.