I made a bunch of isomalt diamonds to use on a wedding cake. I have used them on one other cake but instead of being sparkly, they are clear so they don't really show up. I read one suggestion of painting the backs of them with silver luster dust but that did not do a bit of good. I have seen individual sparkly diamond looking things on wedding cakes but I don't know how they would get them that way using isomalt. Is it possible that people are using individual ones on cakes and they are non-edible? That would be scary to me.
Luster dust maybe?