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Sand Cast, Sand Casting

Sand Cast, Sand Casting.  The casting, or making a cast in a mold made of sand. Because sand casts typically have porous and uneven surfaces they are not suitable for coin models but can be ideal for making medals where a somewhat grainy surface is desired. Sand casts are usually large medallic items, as plaques or foundry cast patterns. An example was the Special Medal of Honor of the National Sculpture Society, where artist Laura Gardin Fraser wanted a more typical sculptural treatment for the glyptic field's highest award medal.

How a sand casting is made.  This is a very old method of metalcasting, however for art casting it is also called the French sand process. Dry sand is mixed with water and this is called green sand. Green sand is used because it can be packed tight and holds together due to the affinity of water between the grains of sand.

The mold is made around the pattern by packing green sand as tightly as possible

(this is accomplished with fingers and a wooden tool called a bench rammer).  Uniface plaques and single sided patterns can be made in an open mold. Such a mold does not have a top on the flask which holds the green sand in place while the mold is made and the metal is poured.  (A diagnostic of an open mold casting would be a reverse with a lightly rippled surface and a slight meniscus at the edge, forming a rounded raised rim.)

To obtain a two-sided casting, or a casting with a core, a bed in the drag (bottom half of the flask) is filled with green sand. The pattern is placed in position, to extend half above the top and it too is packed with green sand. The sand is somewhat bonded because of the water, it is retained in the cope as it is separated from the drag and the pattern carefully removed.

Channels are cut in the green sand, gates, sprues and vents for the metal to enter the cavity and air to escape. The cope is placed back over the drag and clamped together to resist the pressure of the molten metal as it flows into the cavity. Once the flask is ready and the metal heated to the proper temperature, the pour, pouring inserts the molten metal through the sprues into the mold cavity.

The casting is allowed to cool, after which the flask is removed and the sand is

broken away from the casting. It is cleaned and ready to have the metal that filled the gates, sprues and vents removed by cutting and grinding smooth. There will be a parting line where the cope and the drag came together; this along with any other surface imperfections will have to be smoothed out by chasing

The metal at this stage is as-cast, bright and untoned. The surface will have to be treated in some way to prevent rust (for iron castings) or toning (for copper and bronze castings). The metal surface is given a finish to prevent toning and corrosion, and for aesthetic coloring if it is an art object.  See finish and finishing.

Sand casting is the oldest form of metalcasting. It is one of several current methods of casting, the others include diecasting, precision casting (with lost-wax, also known as investment casting), ceramic mold and shell mold, and also permanent mold casting.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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