I wrap it in a soft cloth, put it into a vise edgewise with a plastic bucket underneath with a towel in it, and gradually crank down until I hear it crack. Then I look to see if it's cracked enough to break it the rest of the way by hand and if not, then have another go in the vise.
@lordmarcovan Featured thread.. https://www.cointalk.com/threads/th...hnique-quick-primitive-effective-safe.315594/