The kinds that you get off the shelf typically are made of soapstone or some kind of polished rock that's safe to use in beverages. You just refrigerate the stones in the freezer, and when you're ready, place it in your whisk(e)y glass and pour away. The refrigerated stones will start absorbing the heat from your whisk(e)y, therefore chilling it. Since it's not ice cubes, it will not melt and dilute your whisk(e)y.