Of course there is no way of absolutely securing it against all possible movement, especially something like an earthquake. However, craft stores have styrofoam rings in various diameters that might be useful. I'll leave it to the professional curators and conservators to say whether or not the styrofoam presents a source of degradation to the object.
I am from Kirkland Heritage Society in Kirkland, Wa. We have a fire grenade that is on loan from one of our board members. It is currently in a display case, but not secure. I.E. it can roll around... more
The earliest grenade-type fire extinguishers were invented in the late 1800s were thrown at the flames. Made of clear or colored glass, these extinguishers usually have a fancy cut-glass, round... more