The bowl is constructed on a solid wooden form and it looks like this on the inside when it first comes off the mold.
Next you attach hand-made paper between each joint so that it stays together!
The masking tape shown here is essential before the paper strips are glued on the inside. The green masking tape keeps the joints from splitting and ruining all of the work you put in! Shown at the bottom is a piece of wood connecting all the ribs together. This is called the cap, I chose a piece of yew with a good amount of sap wood for a nice look.
Eric shull Portland luthier 
Wow, that is awesome. Do you know what was used before masking tape, “in the old days”?
I know that when they glued on the soundboard to the bowl the ancient makers would use paper and glue as a clamp to hold the two together, maybe something like that? After taking the bowl off of the mold that they were probably just very careful. One account describes a sort of “false belly” attached to the bowl to hold everything together after being taken off the mold. Here is a link of someone who built a lute using original methods http://www.lutesociety.org/pages/building-lute-original-methods. Some of the methods are surprisingly practical.