While my niece was visiting we played around with the FIMO clay and the molds I’d made earlier in the week. I made a set of black buttons that turned out quite nicely. These have small jump rings embedded in the back as button shanks. I may try something molded on the back next time using a toothpick to bore a hole parallel to the top of the button. I have several metal buttons with that sort of shank and I think it may be sturdier than embedded jump rings.