this great project over at Notcot and decided I had to try it myself with some tweaks.
Cut out geometric shapes from poster board and tape together (very well) leaving the tops open and sealing the inside with the tape (to make it waterproof)
Balance the shapes in a cup or bowl, so that you can pour the concrete in to the top of the molds.
Mix up your plaster - just adding enough water so that it is going to fill the mold- you don't want it too wet or it will never dry or turn your mold in to mush.
Pour that stuff in!
Now is the hardest part - be patient.
Wait at least an hour, but overnight would be better, before peeling the paper off and revealing your new creations!
I used a paring knife to shape the egdes a little more finely. You can also use a file or sandpaper if you're wanting a smoother edge.
You can do a variety of things to the finished plaster gems. Painting, sanding, dipping in plasti-dip, oh, my, the possibilities are endless!
I experimented with painting parts of them a nice copper, and I think they're lovely:
Template from Minieco is here.