Glass jars with white metal caps have a layer of porous plaster poured on the jar bottom. They are shipped without being charged to allow shipment through the mail. Jars in this series are listed in four sizes, and are the preferred type for beginning or young collectors.
Ethyl acetate, see #1185A, a commonly used killing agent, is sold separately. To prepare for use, pour about 1 oz. of ethyl acetate into jars, screw on lid and wait 20 minutes until plaster is fully saturated. Then, using a funnel, pour any liquid remaining on the surface back into the container of ethyl acetate. Recharge jars as needed.