This set uses one of my favourite techniques - hydro-dipping (or marbling).
With this technique, you drip special inks onto the surface of some water to make a pattern, then carefully dip a blank dice down into the water so that the ink folds around it. You then cast the patterned blank in resin to seal it.
I've hydro-dipped paper before. Are there any extra steps for dipping resin?
(Sweet dice, btw)