I once attended a yoga studio class that was a go-anywhere studio where I could breathe and sweat with so many strangers that our mats were only a thumb's width apart. Each time we all ended each day's class by rubbing together a frosted crystal singing bowl that was big enough for 50 people to eat salad. As it sang, I sometimes saw the colors swirl and fade, a virtual tie-dye behind my eyelids.

This bowl takes me back. Afterwards, my busy brain feels cleansed, like I'm using a kind of mind floss. We were supposed to close our eyes until the end, but as our teacher scooped his wand around his lips, stirring up a loud buzz, I peeked in and wondered how it worked.

I discovered that the singing bowl is the ancestor of the bronze standing bell, or inverted bell, which is struck with a wooden mallet to strike a note. Standing bells originated in China during the Shang Dynasty (16th-11th centuries B.C.) and are still used to accompany meditation. Early ones looked like a metal goblet. These were cast from molten metal and then struck by hand into a certain shape and size. Tibetan singing bowls, also made of metal, first appeared around 560-480 BCE.