Gelatin is probably easier, but I don't know how it would hold up on a cake. Isomalt requires heating, etc., so it's more labor-intensive, but it will look more like real stones.
If you have the silicone jewel molds, you can use crushed up jolly rancher or lifesavers
two tricks
1) hard candy mix - its a dry mix (probably Isomalt, but with stabilizers or some sort) mix according to directions
2) coat the outside of the jewel in a bit of oil. And if it gets dull in a few days or a week, renew the oil. It will sparkle again.
I got some three week old "test" stones. A coat of oil and I could use them.
Leah, what type of oil do you use to coat the jewels?
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