Browsing the Gilcrease Museum’s collection of pre-Columbian American art and tools in Tulsa, OK, one keeps coming back to the obsidian knives, arrowheads (or “projectile points,” to anthropologists), and even ear ornaments—glossy black, smooth, and glassy. For tens of thousands of years, indigenous peoples fashioned these items out of cooled lava, beautiful but also able to hold a keen edge for millennia. The same museum collection also features metal knives, some only a few centuries old, already pitted and rusted, and a range of ceramic items in varying stages of deterioration from surprisingly pristine to faded and cracked. Clearly, these different materials—glassy obsidian, earthy ceramic, and metallic—have properties that influence how they stand the test of time.