Plaster powder is a favored art material as it lends itself well for making molds, casts and even shell molds. Both plaster molds and casts capture the details well and set to a smooth and rigid form.
There are many mold making materials like clay, wax, polyurethane rubber, silicone rubber, etc. Similarly, there is no dearth of choice for casting the mold, it ranges from gypsum and resins to various kinds of rubbers. However, only a few materials can double up for making both molds and casts.
Plaster is one such versatile material that is equally suitable for molds and casts. Additionally, plaster bandages are commonly used for making shell or mother molds too.
Let’s take a look at the multipurpose nature of plaster in the world of mold making, casting and life casting –
Molds – Plaster powder is mixed with water to form a fluid paste. This can be applied over the object or poured into a mold box to form a smooth and solid mold. But care is needed as the plaster can deform easily while it is wet. Yet, the mold will capture crisp details without becoming chalky over time. It can also be carved or tooled easily. The same plaster is often used for restoration works as well.
Life casting artists even use plaster for making molds of the hands. All that the model has to do is dip the hand in the container of plaster mix and hold the pose for a while. The hand can be extracted after a while and a negative impression will be left behind.
Casts – The same plaster slip can be poured into a mold to form a figurine, statuary, earthenware or other art casting. It picks the details well and sets quickly to a smooth and rigid form. The cast remains lightweight making it easy to demold, work on and carry around if needed. It also holds the finish well without chipping or cracking over time.
In fact, plaster is considered the ideal medium for making life casts in both alginate and silicone rubber molds. You can choose a bright white, high definition plaster to get a natural white finish.
Shell molds – Gauze strips that are infused with plaster are the material of choice for backing flexible molds, such as those made of alginate or silicone rubber. The same plaster gauze is also applied directly on the human body to make body molds. While the plaster bandages cannot capture fine details and can release heat, they are still suitable for belly molds, especially for pregnancy casting.
Precautions – Keep in mind that you cannot use generic plaster of Paris for artworks as it tends to get flaky and can develop cracks. Special art plaster is available in art stores. It is equally important to mix the plaster and water properly and in the correct ratio to get a smooth and thick blend. Furthermore, avoid working with plaster on humid days as this will extend the drying period.