Often when picking materials for my costumes, I go for the cheapest possible solutions. I did that as well when I made my druid costume, and bought the cheapest resin I could find at that time, which was this one:
Sadly, it was a case of cheap not being as good as the more expensive. I could never quite manage to get the amount of hardener to resin ratio right, and my gems took almost a week to harden. The surfaces were uneven (at the back), there were a lot of bubbles, and some even turned out not clear.
So for the Alex/Ysera costumes, my cosplay partner and I bought another brand, this one:
I was ready to close off my room for a week for this stuff to harden and stop stinking up the place, but actually, the cast was done after just a few hours and it turned out very smooth and clear, so this brand is definitely worth recommending! I bought it from Naturgut seller on ebay.de and had it shipped from Germany. It’s not the cheapest resin, but I think I’m sticking with this in the future – it’s great!