Now I understand that this is not the first time someone has thought of this, but has anyone tried a mortar bowl... (As in mortar and pestle) as a shaving bowl. I know that many can be found in ceramic and marble. I figure that they would hold heat for quite a while and usually have a large bowl for lather, some even have handle holders for the pestle. Does anyone have experience with these or any ideas as to ceramic vs marble etc.?