Cold Cast Bronze - Casting Process
Cold casting is a method of reproducing figures using resin mixed with powdered materials. The resulting pieces have the look and feel of metal, stone, porcelain or wood but without the expense and danger of traditional foundry processes and working with molten materials. Cold casting is safe, quick and cost effective and results in appealing pieces in a variety of finishes.
Creating A Mould
The first stage in the cold casting process is to create a mould from which each piece will be cast. Moulds can be fashioned from rubber, resin or silicone. Silicone is generally the preferred material as it does not require the use of releasing agents. These ensure that the casting material can be easily removed from the mould once it has set and must be applied to rubber moulds before casting. The moulds are created by placing the item to be replicated in a suitable container and mounted on the base of the container with a proprietary glue.
The moulding material, usually silicone rubber, is then poured into the container and around the original piece. Air bubbles can form in the silicone which will result in blemishes and so these must be evacuated either by using a vacuum chamber or pressure pot or by placing the container on a vibrating surface to draw the air bubble up and out of the liquid. When the silicone has set the container can then be cut away. The silicone mould is carefully spliced in two in order to remove the original piece and to create a two part mould. Silicone moulds are then baked to strengthen them and to evaporate any residual alcohol which could interfere with the casting material. The flexible moulds can be used to create a number of replicas but they do degrade during the casting process and so typically each mould can be used from 25 to 100 times before being discarded. A rigid outer shell is then fashioned from plaster or similar to support the mould.
The Casting Process
A wide variety of materials in powdered form can be combined with a resin to be used in the cold casting process. These include bronze, iron, copper, aluminium, wood, marble, onyx, slate and porcelain. Pigment may also be added to the mixture. The first stage of the casting process involves mixing the chosen media with resin. Epoxy, acrylic, urethane and polyester resins can all be used. Urethane resin is most commonly chosen for casting sculptures. Polyester resin shrinks when setting and is utilised when it is desirable to create finished pieces which are smaller than the original work. The chosen powder and resin are mixed in appropriate proportions according to the chosen resin and then vibrated or agitated to remove any air bubbles which would cause blemishes. This must be done quickly as the resin mixture takes only minutes to set.
The mixture of powder and resin can now be used to fill the mould but here there are different methods which can be employed. The two portions of the mould can first be coated with a layer of powder which will adhere to silicone moulds. The layer of power would then be covered by a layer of the powder and resin mixture. A more straightforward method is to begin by simply applying a coat of the resin mixture to both halves of the mould. Using either method, the two portions of the mould are then put together and the void filled. The void can be filled with the same powder and resin mixture used for the initial layer or with a mixture containing less powder. Pure resin can also be used. Heavy materials like sand can be added to the resin or mixture to produce a finished piece of similar weight to solid bronze or marble.
The casting material will set quickly and once it is completely set or cured it can be carefully removed from the mould. There will be small amounts of residue or flashings which must be cleaned from the piece. These are prone to form in the area around the join in the mould.
Finishing
The pieces must then be finished to produce a pleasing and authentic appearance. Metallic castings are polished with fine steel wool. This process removes the resin particles at the surface leaving only the metal. The surface can then be artificially oxidised or weathered using patina acids to create a variety of pleasing finishes. Paints can also be used to produce different effects. If any oxidising or ageing effects are not desirable the piece can be sprayed with clear gloss to preserve the finished look.
Cold casting can be used to produce a variety of decorative and practical pieces including figures and reliefs. It is also a fabulous way of producing replica door and drawer handles and knobs if exact replacements cannot be found.
Cold Cast Pieces from Sculpture Gallery
Cold casting perfectly captures the beauty of original sculptures and produces fine, affordable replicas for collectors to enjoy. The Sculpture Gallery range features many excellent examples of cold cast pieces. The artists whose work is available as cold cast sculptures include Paul Jenkins (bronze), Veronica Ballan (bronze) and Doug Hyde (porcelain).. We hope that this guide has given you some valuable insight into the cold casting process. If you are interested in other casting techniques and would like to know more about the lost wax method then click here to see our guide.