You can use sharp stuff in these bottlecaps as long as the pointy bits are completely encased in the resin. I like to have some stuff that sticks out, like the tiny fuse and the top of the push pin. The blue bead in the bottom is from some canes I made during a polymer clay session a couple years ago.
I thought about selling these, but then tallied up the cost of the materials, and realized I would make about fifteen cents per magnet if I sold them for a buck each. I’d rather keep them and give them as gifts than use my labor to make money for some retailer.