It sounds like a wonderful group of beads are now yours! The sparkly metallic effect inside your sommersos is indeed tiny copper particles, the same sort which are suspended in the "drizzles" or trail decor upon the "wedding cake" beads.....over at Google translate, "sommerso" translates to "submerged"...take a 14x loupe to your beads, it will be interesting.

The fancy Venetian beads that are decorated with gold leaf on the OUTSIDE are a different animal entirely. This exterior decor is very fragile, and should be handled with extreme care. Don't sleep in them like I do many of my beads. You can almost visibly rub this gold foil off, which is why examples that have survived for decades in great condition are rare.

Yet another effect is indeed gold leaf inside, or underneath clear glass. I have some plain ones like this. They are an irregular shape, with the bright gold foil protected by clear glass. But it looks nothing like the sparkly aventurine of "sommerso" beads.

Confusing, I know , but hope this helps.