Our Colored Crystal Singing Bowls are manufactured from 99.99% pure quartz crystal, and are the finest, pristine, crystal singing bowls. The crushed quartz is heated to at least 1800 degrees in the manufacturing. Then, they are tested to determine the musical note. Although the larger bowls have a deeper, lower octave, tone, it is not the size that determines the 'note' of the bowl. The bowls are associated with the musical scale, starting with C, then D, E, F, G, A and B. These notes are in turn associated with the Seven Chakras of the Human System.