Bottles and Fusible glass
Bottles made today are more nearly compatible with float glass than any other. Older bottles may have all kinds of compositions.
It might be best just to layer the scraps on the shelf and try fusing them together without a base. I had a student from art college trying to make sheets from broken bottles found at teen age drinking dens. Even these bottles produced at similar times, but from different sources, showed a lot of stress when fused. Although they stayed together for a time, only a few made it through the slumping process.