A crystal singing bowl is a bowl of fused quartz, almost pure silica, that rings with a clear, steady tone when you strike it or rub a suede mallet around its rim.
Most frosted bowls start as quartz sand poured into a spinning mold. The sand is pressed against the wall by the spin and fused with an electric arc at around 2,000 °C, which leaves the inside smooth and the outside white and grainy. The technique comes from industry: the first bowls were crucibles of the kind used to grow silicon crystals for computer chips, and sound healers took them up in the 1980s. Clear bowls, colored bowls and bowls with metals or gemstones fused into the glass came later.
Quartz loses very little energy as it vibrates, so a bowl keeps ringing long after it is struck, and almost all of that energy goes into one mode: the rim flexing into a slight oval, then the other way, hundreds of times a second. You hear that as a nearly pure tone, with much less of the clangorous overtones of a metal bowl. A real bowl is never perfectly round, so the tone is two pitches a hair apart, which gives a slow, gentle pulse.
Bowls are usually sold in sets of seven, one per note of a major scale, and each note is matched to one of the seven chakras of the yogic body, C for the root up to B for the crown, each with its traditional color. This pairing is a modern convention from the sound-healing world: the old texts on chakras do not assign them musical notes.
Some sets are tuned with A at 432 Hz instead of the standard 440 Hz, which makes every note about a third of a semitone lower. Others are tuned to the Solfeggio frequencies (396, 417, 528, 639, 741 and 852 Hz), a set of numbers popularized in the 1970s and 1990s and said to come from a medieval hymn. The hymn gave us the syllables ut, re, mi, fa, sol, la, but medieval singers had no fixed frequencies, so the numbers are a modern invention.
In a sound bath, people lie down and listen to bowls, gongs and chimes. Many find it deeply relaxing, and small studies report short-term drops in tension and better mood. There is no good evidence that particular frequencies heal particular organs or conditions, so it is best enjoyed as a way to rest and listen.
The bowls here are not recordings. Each one is synthesized in your browser from a few sine waves: a long-lasting fundamental with a slow beat, a faint overtone at about 2.8 times the pitch, and, when you sing a bowl, a whisper of filtered noise for the suede on the glass. The water is a simple drawing of that lowest mode, not a fluid simulation.