[iacopo.russo (OP)]

Marcos wrote to us to ask:

I am curious about the process of melting gold into glass. Why if you mix it with clear glass you get red-cranberry glass, but if you melt it with blue glass, you get saphiret? Also, what is the technique for recreating saphiret? I can't find A SINGLE ARTICLE on the "how", all topics are all about the "what"... Is it mixed up in the crucible? At what point? How does one work with it once created? What are the steps for, say, cabochon/chaton making? How long does it need to be annealed? I have more questions too, about foiling the back of the glass stones too, but I wanted to stick with the basics to start.. thank you!

Can anyone help?

[Bored chemist]

Well, for a start this is what actually makes the glass red.
https://en.wikipedia.org/wiki/Colloidal_gold

You make it by mixing gold chloride (not the metal) with the glass.

[JesWade21]

THIS! A professor of mine actually made it a point of explaining the different aspects of this in the course of my Radiation Safety class! A lot of people don't know the reasons behind what happens and what shouldn't be put on demonstration without understanding and explanation to explain the reasons behind them!

[vhfpmr]

gold chloride

Well you learn something new every day. I'd always thought that the reason gold doesn't tarnish is that it's completely inert, and won't form compounds. Dunno where I got it from, school probably.

[SeanB]

Gold does react chemically, just that normally it is hard to get it into the ionic state, so typically those kind of reactions start with dissolving the gold first in aqua regia, where the mix of nitric and hydrochloric acid enables the gold to dissolve into the nitric acid, and then stay as a relatively stable gold acid thanks to the hydrochloric acid. Just normally gold is very insoluble in anything other than strong acids, so mostly occurs as a metal or a very low concentration of ions.

[Bored chemist]

You can dissolve gold with ferric chloride or with tincture of iodine.
You need an oxidant and a source of some complexing  agent- chloride ions are the easiest to get.
You don't need a particularly strong acid.
And many or most strong acids won't dissolve gold.

[gem]

Hi Marcos,

Quite a while ago I bought a piece of art from these people local to me, which I believe utilizes some of the specialist techniques/knowledge you are requesting.
 
https://www.greenhalghglass.co.uk/gallery.html