Looking at the tortilla from the side, you can see how it got all puffy as it was heated up.  The bubbles can be up to an inch thick, which is pretty impressive for a tortilla that started out as thin as John Waters' moustache.

In this case, things turned out well.  The tortilla gained some nice depth, which was perfect when combined with my delicate handling of the original painting.  

But over the next few weeks, the warping got worse.  Check out the demonstration called The Ravages of Time to see what happened.