So I started by shaping the buttons and using a needle to make the holes.
Then I baked them. For this particular clay, you bake it for 15 minutes at 325.
Then I dug out some sand paper and sanded down the buttons once they were hard.
I then painted them...
I haven't actually sewn them on yet, but this is what I'm gonna do with the black and red ones. The others I'll probably reserve for slippers I make.