The sound given off by singing bowls is a result of vibration. Let's take a look now at mechanical vibrations apart from the sonic properties of the bowl.
You could alter the roughness of the bowl's vibrations from rough to finer by changing your playing style (not applicable to every bowl). If you rub a mallet covered with suede on the lower part of the rim (going parallel with the mallet to the wall), you'll most likely produce the rough vibrations. If you lift your mallet and make a sharp angle relative to the edge of the rim and press the mallet harder, the vibrations will go finer. As a result, the sound will change from a low tone, (roaring like refrigerator) to a higher "singing" tone.
There is a category of singing bowls that I call "Massaging bowls". These bowls have really smooth and sensible mechanical vibrations and as you might have guessed by now, are good to place on the body for a nice massage. Some of these bowls are also perfect for reflexology.
A massaging bowl should be medium or large size but lightweight and should produce a smooth and relaxing low tone that is barely noticeable. At the same time, the bowl could (not must) be able to play high pitch as well (if you'd like to offer to the client a change of mental and emotional states).One of the marks you'll see attached to the bowl's description is "M", means massaging properties. The scale is 1-5. The higher the number, the more sensible are the vibrations of the instrument.