The dark glass is the core of the bead. The molten glass is rolled over frit, which is chips, crumbs, or chunks of colored glass. The blob is reheated and shaped.

End-of-day is a misnomer. Such beads were created intentionally in particular color combinations and frit size, not just from leftovers. Yes, scrap glass might be used to form the frit, but these are a product line.