NNP

Release Agent.  A coating in a mold to ease the removal of a casting; a mold release. Release agents are also called parting agents and are used in most all casting applications irrespective of the type of mold or the composition of the casting. (Green sand castings are the only molds which do not need a mold release, because of the water in the sand.)

In electrogalvanic casting the release agent of bronze powders metallizes the surface, not only does the bronze powder coat the surface of the object to be cast but also makes the surface electrically conductive for the deposition of the metal. Clay models are usually coated with talc but graphite can also be used. Plaster models are coated with green soap when pouring other plasters in the casting, but light oil, silicon spray can also be used as release agents. See plaster casting.

Casting mold preparation.  The ideal surface to be cast is one that has no pores, is very hard, has no undercuts and all relief and lettering has a bevel of 5° or more. Plaques to be cast in flexible molds do not require the latter two. The hardest, finest plaster is used for coin and medal models (as Densite). Any organic material (as wood or ivory) has pores; these need to be closed off. The face of the mold is coated with shellac.

After the pattern is as hard as it can be and all pores are covered over, then the mold release is applied. Messy powders, as graphite and bronze powders, are applied with a brush. A stipple brush is used for green soap on plaster, light oil is applied with a cloth. Liquids that can be sprayed on are the easiest, but are susceptible to applying too heavy a coating. Theoretically only two microns of coating are needed for separating the mold and its casting. Release coatings need only a very light coating but it must cover the entire surface.

Pattern or Mold       Release Agent         Casting 
Composition                                                     Composition

Clay or Plasticine      Graphite (plumbago) Plaster
or talc Plaster

Epoxy                             Silicon spray                Plaster, metal

Galvano Patterns             Bronze powders                Electrodeposition:
metal, plaster,                                                            Copper, silver,
epoxy                                                                        gold

Gelatin                           Alum (for hardness)         Plaster

Green sand                     None required                  Usually metal

Plaster                           Green soap, light               Plaster, metal
oil, commercial
mold release

Rubber, Latex,                Silicon spray                     Plaster, metal
PVC

Wax                              Plaster, metal

Wood, Ivory       Shellac (for              Plaster, metal
                                      sealing pores)

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON