I don't know, but perhaps that the idea is for foods to cook more evenly, instead of having the edges overcooking while the middle is still "sad" (underbaked).

Or maybe the idea is to compensate for baked goods that rise in the middle... think of a cake baked in a flat pan- it's taller in the middle and shorter along the edges. I've seen recipes for layer cakes that call for the baker to use a knife to slice off the "dome" in the middle of the cake so that all the layers of the cake will stack evenly.

It would be interesting to bake a single-layer cake in the pan and see if the cake is more uniform in height than cakes baked in a flat cake pan...

Good luck,
Virginia

I'll have to do that and see. Seems like it would make the middle twice as high as the edges.

Guess would be:
if the pan is really old and the convex bottom shape variation is fairly minor, it was probably a design feature to try to reduce stress from rapid heating and cooling which could otherwise cause breakage. There are a few mentions of very early attempts by companies to produce something that was a forerunner of the Corning Vision line using a convex bottom. The Items were somewhat problematic and consumer acceptance was not great. It might be a good idea to junk it or at least never use it for baking or on a stove top.

I have 3 of these convex bottom clear glass pie plates. Mine are huge - almost 13 inches rim to rim and a 10 inch bottom. I'm thinking industrial.

I'm thinking that the purpose of the bottom is to help cook the middle of the pie. It would be thinner than the edges and thus cook faster.