At some point, the Paleo-Indians realized they could use the heat rising from holes in the caldera floor to melt the glass and metal chards they collected. They used the molten materials and recast them into their standard tool shapes.
Over centuries and perhaps eons, they became highly skilled at glassmaking. Eventually there were able to place an ash shaped image of the animal represented by the tool, inside of the tool. Look closely at glasswork pieces that have black areas inside of the glass.