Casting and molding are fundamental techniques that have myriad applications. They are essential to artists, as well as to the crafts industry. Beyond the arts world, many industries rely on casting and molding to produce their signature products. We are surrounded by objects that are the end result of these two processes -- children's toys, candy and chocolates, household items, electronic equipment, and many others.
Molding is the process by which we take an object and create an impression of it in some sort of material. Generally, an initially soft material is poured or spread around the object and allowed to harden or set, creating a negative imprint of the object. Depending on the shape of the object and the nature of the molding material, a mold can be made in one piece (for an object such as a flat medallion, for example) or in multiple pieces (for something like a complex sculpture with many undercuts).
Common molding materials
The best material for molding a particular object depends on the size and shape of that object, as well as what the object is made of. Plaster is a common and cheap material that results in hard, heavy and inflexible molds. If the object being molded is complex and inflexible, you may opt for a softer molding material like polysulfide or polyurethane rubber, or silicone. Special, nontoxic and safe compounds also exist for molding body parts and direct application to skin.
Casting is done once a mold of an object is available. If the mold is made up of multiple pieces, it is put together securely and the casting material is applied. It can be poured in or injected, sometimes through multiple openings if the mold is particularly complex. Allow the material to cure, and then open the mold. Casting creates an exact replica of the object that was molded. Generally, only minor adjustments, such as sanding of seam lines, are needed in the castings.
Common casting materials
Many casting materials are available, including the same ones that are used in molding. Several varieties of gypsum and plaster are frequently used to cast decorative items. Plastic of many varieties is used. Wax can be used to cast items such as candles. Make pottery and dining sets by casting porcelain and glass. You can also cast edible items such as liquid chocolate and candy. Metals can be melted and cast to create jewelry, tools and equipment. The special effects industry frequently uses common molding materials like silicone to cast lifelike models.