You may have seen something like this before - using polarized light to show how a material deforms under stress. I hadn't heard anyone using this technique on gelatin before, so I just had to try it out myself. What a lovely effect. There was som über geekery to be had when we noticed you could easily produce interference patterns. I'll be providing you some more details for tomorrow's demo, but here's a peek into what's going on in the dirt lab:
For all of you strain junkies out there: I'm thinking we are looking at longitudinal strain effects at first - these spread out to a maximum distance quickly and are then overtaken by the transverse surface waves as they radiate outward. Lockwood (Outside the Interzone) mentioned that he had disabled embedded video to reduce computer issues he was having, so here's a still from one of the experiments - this way even those without video capabilities can see what's going on.