Plaster is one of the most commonly used casting materials as it is quite cheap, versatile, readily available, and user-friendly.. Once you start working with plaster, you will realize that it is easy to mix, sets quickly to a pleasant white color, can be sculpted and with proper pouring and application can yields few air bubbles in the cast. In fact, it suits almost all kinds of casting applications.
Little wonder then that plaster casting is especially popular among artists and life casters alike.
Plaster is manufactured as a dry powder and is mixed with water to form a paste or slurry The reaction with water creates heat through crystallization and the hydratedplaster then hardens. Let’s take a look at the role of plaster in regular mold making and casting works:
Life casting –
While plaster cannot be used directly on the skin for making body molds, due to excessive heat during curing, the heat from the chemical reaction does not affect the casts in any way. In fact, you will find that most life casting artists favor plaster as the material of choice when making the final cast from the body molds. Plaster is also favored for casting using alginate, resin and silicone molds.
Latex casts –
Due to the naturally porous characteristics of plaster, plaster molds are widely used in latex casting – such as making latex masks. This is because plaster will absorb the water from the latex and let it cure like a thin skin.
Shell molds –
Alginate and rubber molds need rigidity to support their form during the mold making process. This is done by added a mother mold or shell mold. Plaster bandages are regularly used to reinforce alginate body molds and other rubber molds for this purpose, thus forming the shell or mother mold.
These plaster bandages come in long rolls and are formulated to become creamy with plaster consistency when wet. All you have to do is roll out the dry bandage, cut it to length, dip in warm water, squeeze lightly, and then apply over the original mold. Keep smoothing it down to prevent bubbles in the mold later. You should keep overlapping about half or one-third of the previous bandage so as to create a strong shell mold. The bandages will set quickly enough in 15-20 minutes.
Rough molds –
Plaster bandages are sometimes even placed directly on the body to make molds. They have to be rolled out, wetted and applied carefully. Finally, fold the bandage in quarters to make rope-like lengths. Use it to reinforce the edges of the mold and make a secure mold.
Keep in mind that while plaster is renowned for capturing intricate details well, the plaster bandages will only capture the form and not the detail. However, they are skin-safe and will not cause any kind of discomfort to the model. It is often used for belly casting or pregnancy molds.
Above all, do not be mistaken that regular plaster or Plaster of Paris can be used for plaster casting. That is because plaster of Paris is formuled for application to wallsit is naturally soft and chalky and does not hold detail well. You need to purchase specially-treated and high definition plaster powder that will not chalk, chip or crack. Only then can you get durable molds and casts that hold finishes well and set hard on drying.
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