To see more and discover the full range of casts we do in every material visit the Examples page.
Plaster of Paris
We use a specially formulated hemihydrate plaster (CaSO4.1/2H2O) produced from naturally occurring high purity gypsum deposits. The hydration of plaster relies on the reaction of water with the dehydrated or partially hydrated calcium sulphate present in the plaster. Ours is pure white in colour and extremely hard with very fine reproduction of detail.
Plaster is suitable for small to medium sized castings only. Over a certain size plaster’s own weight and fragility work against it. It is old technology which although suitable for some types of castings has long been superseded by more durable resins, which are easier to work with and more robust. Since you are only going to do this once we would recommend considering fibreglass resin over plaster to avoid the disappointment of breakage. Plaster casts may be larger, however, if they are protected by a frame.
Commissioned plaster casts will generally show the skin texture which is often exaggerated by the alginate moulding material that goes on the body, since it is mixed with cold water. On smaller, cheaper casts the goose flesh is not so noticeable but on larger castings we are better able to smooth them away when we work in fibreglass. We can smooth the surface but our ability to do so in plaster in limited. However plaster casts for sale in the shop do have a smooth surface since they are reproductions of casts originally created in resin.
Plaster of Paris is also used to impregnate gauze bandages to make a sculpting material known as plaster bandages. It is used similarly to clay, as it is easily shaped when wet, yet sets into a resilient and lightweight structure. This is the material that was (and sometimes still is) used to make classic plaster casts to set broken bones. We use it when moulding the body to form a hard shell over the flexible alginate layer in order to maintain the proper shape of the mould. See the How We Do It page to see the process in action.
Plaster is the common name for calcium sulphate hemi hydrate made by heating the mineral gypsum, the common name for sulphate of lime. Plaster was first made about 9000 years ago, and has been used by ancient Egyptian, Greek and Roman civilizations. However, it wasn’t used on a large scale until 1700s, when it was required to be used in all construction in Paris after the 1666 fire which destroyed many parts of London. In the aftermath, the king of France ordered that all walls made of wood in Paris be immediately covered with plaster, as a protection against such fires. This resulted in large-scale mining of gypsum which was available around Paris in huge quantities. Thus, during the early 18th century, Paris became the centre of plaster production, and hence the name, “Plaster of Paris”.