These cards are on photo paper which I mounted on a slightly larger cardstock card base. Since I didn't clean the cookie cutters after using the gold, they've got a slight golden frame which was a super nice surprise:

I tried to do a red and green card, but complementary colors get really muddy when they mix. I liked the pink-blue-green colors a lot better:

Making larger golden bubbles proved to be really difficult. At first I only got small splatters and spots and then I realized that it only works at the very beginning when the mixture is not quite foamed yet:

For the black-gold cards I've used Ecoline Liquid Watercolor in Gold and Mixed Media Paper ("Paint ON" by Clairfontaine). Apart from the photo paper this has also been a great combination, and surprisingly the color didn't bleed:

Hopefully this gives you more inspiration for your own class project! Have fun and experiment!