here is a list of what can be used on an Eternal Item or Pet. I believe Calcite is the only Crystal that can be used on an Eternal Pet.
putting a Myth Stone on an item, or Converting/Salvaging Myth Stones, and I think taking them off of an item, will give a chance to reveal part of a Mythic Recipe. the lowest MS gives the lowest chance for a hint, and the highest gives the best chance.
I just kept using Myth Stones, and every once in awhile a Mythic Recipe would be revealed. I looked in the Forums for a list of Recipes, and I think I used one of them, but all the rest I just waited until one was revealed.