Basically it is a double walled bowl. Pour hot water into the spout... and then make your lather.
By the time you come back for the second and third pass the brush and lather is still deliciously warm on your face.
He has some rather nice looking stuff, and it doesn't seem overly expensive, though I don't know what anyone else sells scuttles for, if I hot lathered I might be tempted to trade in my double bowl set up.