adding gold to batch
I was doing some research for my art history class at Alfred University and I came across a cage cup known as the Lycurgus Cup. The green photo is when the cup is lit from the front and the red photo is back lit. I was reading about the composition and it has about .0005% gold as well as silver and manganese. I'm wondering how one adds gold to glass batch. I know you have to dissolve the gold in aqua regia (very nasty). From there, historically, tin has been added to make Purple of Cassius which I believe is a powder. However, on Instagram, I saw a post where someone poured a solution, I don't know if this was the aqua regia with auric chloride or something else like a gold solution with some thing else added, straight onto the batch which was then mixed and other oxides added.
I'm really interested in this because this is a glass that becomes completely different based on how its viewed. There's a duality to the glass, similar to rare earth glasses that change color or uv reactive glasses like uranium.