Old Ceramic Wotsit

Emergency Blip time. This thing appeared in the garden a few months ago. What could it be? It’s like a big bottle, but it has a stopper halfway up the side. It comes from an age before plastic and possibly even rubber.
It’s a ceramic bed warmer. You filled it with boiling hot water and moved it around on the bed to take the chill off. Most likely you got the chamber maid to do it in some households.