The white layer on top is the gasket for the base cylinder. It keeps air from escaping in ways you don't want it to.
The grey layer below is the gap between the base plate and whatever surface it was resting on. It's grey because the engine blocks all but the stray light that manages to bounce around between the surface and the reflective base plate.
Everything in between is the stainless steel plate, maybe 1mm thick.
At least I think it's stainless steel.
