The "aventurine" in the Perth cylinder vase (and the chalice), isn't copper or gold coloured, it's the colour of bronze, and all clustered around the bubbles, so it must have been particulate within the molten glass.
(I saw a fascinating science programme about bubbles in liquids not too long ago; and how particulate matter will adhere to the surfaces of bubbles in liquids, and while the programme was more about using this phenomenon along with ultrasonics, to deliver drugs directly to the point of interest, but it was
very relevant to the formation of bubbles in glass, and how we end up with enamel haloes around them. )
I've not a clue what it might be. It's not copper, or gold, or mica flakes from Woollies.