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Definition of Casting Molds, Especially as Used for Miniatures and Collectibles

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Two silicone molds for gaming scale castle parts along with some parts made in the mold.

Photo showing a Hirst Arts silicone mold filled with plaster, and an empty mold along with some cast parts.

Photo copyright 2008 Lesley Shepherd, Licensed to About.com Inc.
Definition:

A mold, also interchangeably spelled mould (more commonly seen in use outside of the US), is a hollowed shape, formed around an original object or part of an original object and used to cast duplicates of the object or its parts. Moulds can be made from a number of materials, including plaster, metal and silicone, which are the forms most often used with miniatures and models.

Manufacturers often use the same mold to produce different painted variations of their products. For this reason, collectible model horses may be referred to by "mold number", as in "mold number 485" a Friesian horse mold based on a sculpture by J.M. Herrick for Breyer, in order to identify the shape of the collectible, when the finish can be very different and used for several variations of an object made for sale.

Condition of collectible objects is often based on the mold lines and crispness of the finished piece as it is presented for sale. Casts made early in the use of a mold are often much crisper, with higher definition, than molds made later in the use of the mold. For this reason, limited edition pieces made in molds may have a higher value with a lower mold number listed. Edition # 20, may have much crisper lines than edition #300, depending on the detail of the original and the type of material being molded.

Moulds can be made for one side of an object, or can be designed in parts combined to easily come off the finished cast in several directions. There are a range of Types of Simple Moulds easily made and used to cast a few copies of a hobbiest's originals. Many companies produce a range of molds for making miniatures, including Push Molds for miniature building parts, miniature dolls and miniature food.

Molds come in several variations:

  • Spin Cast Molds - often made of silicon, are used with centrifugal casting to make metal and resin miniatures, often gaming figures, and various types of model horses. They are also used for production of plastic figures.
  • Injection Molds - are used with liquid plastics to produce parts for many plastic models and action figures,
  • Plaster Molds - are a common pottery and china mold, easily made and used mainly with materials which shrink when drying. Pottery molds made from plaster absorb some of the water from the clay mixture, helping to cause the pottery to set to the 'greenware' or unfired stage.
  • Silicon Molds - are flexible molds made from two part cure silicones, often used where a highly detailed flexible mold is required due to extreme 'undercuts' in the design of the original. The simplest silicone molds can be made with two part silicone mold putty.

In addition to types of molds, you will also often find reference to Mold release agents. These are the substances used to prevent the mold to sticking to the casting material. Silicone molds generally do not require mold release agents, nor do plaster molds used to cast materials which shrink as they dry , like clay or pottery slips. Common release agents for molds include spray oils, talcum powder, and for some types of polymer clay, a spritz of water.

Also Known As: The words mold and mould are used interchangeably for groups of fungi, slime and water molds (protists) and types of garden compost made from leaves, as well as their use for forms used for casting, in both art and industrial contexts.
Alternate Spellings: mold, mould
Common Misspellings: mowld, moold, muld, moweld
Examples:

With a simple silicon mold you can easily cast bricks, blocks and other parts for miniature buildings.

Mold #485 has been used to create Jack Frost the 1999 Breyer Holiday Horse

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