For several years I found sculptural use for the flat copper rings that are used as gaskets in ultra-high vacuum systems.  These rings are of well-annealed copper and conform easily to the shape of the joint that is to be sealed – but the copper undergoes work hardening when it is first squeezed for joint sealing so the gasket can be used only once.  Because these joints are frequently opened in our research laboratories, I am able to pick the ones I need from the steady stream of  once-used gaskets destined for the recycling facility.