Casting resin is generally either made of polyurethane or epoxy. Epoxy casting resin has the advantage of curing to a clear, glass-like state. Its curing time is longer, requiring anywhere from 24 to 48 hours to cure. Casting large amounts of epoxy resin may result in cloudiness within the piece. Because of this, epoxy casting resin is usually used for smaller pieces. While polyurethane casting resin is more suited for larger pieces, it is more opaque than epoxy resin. Polyurethane resin also takes less time to cure.
Two-part casting resins are used to cast objects from premade molds, generally made from silicone or latex. When the resin is mixed with an equal amount of hardener, the two parts create a chemical reaction that causes heat to build up within the mixture. This heat catalyzes the mixture to form a solid object. Depending on the type of resin, the curing process can take anywhere from a few minutes to more than 24 hours. Once the piece has been cured, it can be removed from the mold and will retain the detail and shape taken from the mold.
Two-part casting resins can be used for a number of different applications. One of the most common uses for casting resin is the replication of original objects. In this process, a mold is made, based on the original object, and the resin is then poured into the mold and allowed to cure. Two-part casting resins can also be used with specially manufactured molds that allow for casting of items such as jewelry pendants, drawer knobs and bangle bracelets.
When using two-part casting resins, a number of problems can arise that may result in an unstable cure. Because of its one to one mixture, it is essential that the two parts are thoroughly mixed and properly balanced. When dealing with an unbalanced mixture or one that has not been mixed properly, the resin will remain tacky after curing or it may sometimes fail to cure at all. Another common problem is curing temperatures. Because casting resin requires substantial heat to cure, allowing a piece to cure in an area that is too cold can cause the piece to cure improperly.
Two-part casting resin contains toxic chemicals. When mixing and pouring, work in a well-ventilated area, preferably outside. Because of its toxic nature, keep all materials used for two-part resin casting out of reach of young children and pets.