A plaster is the model made during the design process of a coin or medal. They are sculpted in a much larger size than the actual size of the final coin or medal. Plaster casts can be positive or negative and the artist is able to add or carve additional detail. Plasters are often mounted on wood and become a very desirable wall hanging.
The Peace Dollar plaster pictured here is an incredible discovery as it is not only the only known plaster for de Francisci's 1921 Peace Dollar, it is also mentioned in the history of the Peace Dollar. It is 8 3/4" diameter and 1 1/4" thick, a common size for plaster models, and one can imagine evaluating designs at this scale.