When making wooden bowls the woodturner enters a world of creation that is thousand of years old. People have been using bowls for a long time and making them just as long. The same design questions that face the potter also face the woodturner. One of these is just how thin or how thick to make the vessel walls. Some questions need to be answered to give some guidelines.
First of all there is the intended use of the bowl. Is it going to be functional such as a salad bowl or is the intention to be visual as an art piece? Generally, a functional bowl will be thicker so as to give stability and a sense of security. Artistic turnings may be extremely thin to give a sensation of lightness and perhaps an ephemeral quality. On the other hand a different artistic turning may be very thick and heavy to present other feelings and qualities to the beholder.
A third category may be a bowl made to impress and perhaps to impress woodturners in particular. In that case it may be so thin as to allow light to pass through the oiled wood. To make one of these, woodturners hang lights behind the turning piece and thin the bowl to allow an even distribution of light through the walls. It is a good test of skill and a learning experience.
Functional bowls should have walls that are thin enough to work with the intention of the piece and thick enough to seem right. As a rule of thumb and eighth of an inch of thickness for every inch of diameter seems about right with a bit more for six inches and under and a bit less for bowls over sixteen inches. So an eight inch bowl might be one quarter inch thick while a six inch bowl could be three sixteenths and a sixteen inch bowl, three eighths. Most of the time the best thing to do is not to worry about the exact measurement so much as the look and feel.
Where the bowl is to be used is also a consideration. Restaurants may have a certain criteria they want followed while a bowl turned for the outdoor deck on a summer night might have walls an inch thick. The popcorn may blow away but the bowl will still be there.
Most of the time the best thing to do is relax and make the bowl. If the lines look good and the bowl feels right, chances are the design is good. Sometimes all the practise pays off and the bowl looks absolutely fabulous. The hunt make all the turning just that bit more special.