At first sight this does not look like a turned item. See David’s picture top left. The central semi-circular tube is actually hollow and forms a bowl capped at either end. The “trick” is to create a shape, cut it in half, glue the two sides to one another and then finish it by capping the two orifices created from the two halves of the central ring.
The semi-circular canal is produced using a precut circular template of the right size with the diameter marked across it. One cut and check as you get close until fitting the template into the groove allows no light to shine through when a torch is held underneath (bottom right). Jason also showed one of his pieces at the day which had adorned the back cover (an extremely prestigious location in magazine publishing) of the American Woodturners magazine (top right).
The basic shape turned is shown in the lower left pictures. To do this Jason bolts the wood to a piece of plywood and turns the two sides of the piece. However this is where the incredibly difficult bit occurs. For the basic idea to work the inner surface of the hollowed ring MUST BE perfectly semicircular, so that when the two halves are “folded over” they form an actual circle into which a collar can be fitted to which a pair of lids can be fitted.
Jason went through the process up to the production of the semi-circular canal and then showed the rest as a slide show as cutting, gluing, waiting and then doing all the hand finishing clearly takes several hours.