Ever wondered why those bags are called hot water 'Bottles?'
Well, my aunt had a heritage hottie from (at least) her mother, and which was made from pottery. It was as big as a loaf of bread and had a knob on one end for handling, and a ceramic screw-plug on top.

It was a guaranteed wake-you-up if you touched it during the night.

I just thought you ought to know that. ;-)