Well,  I finally got a barrette made with a herkimer diamond.  I am pleased with how it looks but the Herkimer did crack a little in the process.  The crack is hard to see but it is across the center of the stone and I am very aware of it.

Herkimer Diamond Barrette

I will find a glue that works with the Herkimers and the polymer clay.  That way I can design the barrettes and then add them to the clay after baking.