Hello Nepi good morning and good morning Isabelle
The price that you have looked at is correct except that when it quoted the price for one gallon; it is one gallon of each, hardener and epoxy, so you would get 2 gallons for that price, the same for the 10 gal deal, you would get 20 gallons for that price ($ 498), this is the kind of epoxy where the amount of hardener and epoxy are the same.
Mixing the epoxy, measure equal amount of hardener and epoxy (one to one ratio)
Mix thoroughly
Ad your oxide and crushed crystals
When it is thick pour it in the molds
One of the benefit that I find with this (one to one thick epoxy 150) is that it gives me a long time to work, because according to the temperature it will take 8 to 12 hours to harden, Some of the polyester resin will harden within a half hour
For the plaster you use only some crushed crystal, plaster and water, no metal ( or just a pinch of copper powder but not no necessary)and it will harden within a half hour
For the Orgonite you use resin, metal and crystal
Hope this is of help
josh