I have been playing with gold ink! Found a demo of bamboo online – I don’t love her brush method (I am sure that is not the best way to paint the stems) but the gold ink looked interesting. I found it on Ebay and here. As it is imported from USA, watch out for delivery costs. I used Ebay (Gettycrafts) and it arrived within 3 weeks.
The gold takes a few moments to emerge, as the ink sinks into the paper. And with dilution, the gold is of course less intense – see the test below. So I feel it lacks the subtlety for a full painting, but would be great for cards.