Drop-in. Lead, solder or other base metal which is employed as a filler between two shells, electrotypes, or embossed sides to make a "solid" medal. Or, it is applied to the back of an electroform. In all instances adding this supplemental metal is done to add strength to the piece. Since most shells or electroforms are fairly thin – less than 1/8th inch – they can be strengthened by this metal backing. See electrotype.
excerpted with permission from
An Encyclopedia of Coin and Medal Technology
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor