I always thought the idea of baking a shell was to have a golden variety of
the original shell, which in reality would be worth  a lot of money. Sort of
like the edingeri with rosselli. John is correct, there are few Cypraea that
have the size and markings that would allow them to be passed off as
aurantium, no matter how well they are baked.

I have seen a Cypraea mappa that was doctored to resemble a Cypraea
aurantium. They paint and bake them, not to change the color, but to set the
paint they use to doctor the color of the mappa.

Frank in the land of Pilgrims (Some people say they can't tell the difference
between me and the turkey)