When you think about making casts, one of the first materials that come to mind is plaster. Indeed, plaster is one of the most commonly used casting materials as it suits almost all kinds of casting applications.
Casting plaster is a water based material which is both easy to mix and simple to work with. Furthermore, it is cheap, readily available and sets quickly which further adds to its popularity in the world of mold making and casting. In fact, life casting artists invariably opt for plaster as their final casting medium. Not only this, bandages made from plaster are regularly used to support alginate or even rubber molds and thus form mother molds. Plaster bandages are sometimes even placed directly on the body to make molds like in the case of belly casting.
But, the soft and chalky nature of regular plaster is not entirely suitable for plaster casting. This is why additives like lime, cement, magnesium oxide and glass fillers are added to regular plaster to improve its strength, resistance, durability and permeability and thus make it better cast-able. The plaster is also treated with heat and the final substance yields crisp detail and can be sculpted easily as well. Here is more on 漆喰 look at our webpage.
Coming to the actual plaster casting, plaster is quite user friendly but needs to be mixed properly. It has to be mixed with water, in a large bucket to avoid accidental spillage. Use the traditional time tested method for mixing-the "island meth." Measure out the water needed in a large pocket. Then slowly add the powdered plaster to the surface. Continue adding until the plaster forms an "island" in the center of the pocket and covers 2/3rds of the surface. You are best off mixing by hand (use rubber gloves) so you can feel and crush any lumps. The mixture should be smooth and about the viscosity between heavy cream and yogurt.
If you are using traditional casting plaster (as opposed to quick setting dental plaster) another benefit in plaster casting is that plaster takes about half an hour to set, so you don't have to unnecessarily rush with the casting process. But you also have to be careful as plaster undergoes a chemical reaction which makes it heat up while setting. In a krage quantity, this can even burn the skin and that's why plaster is used only for casting and not applied directly on the face or other body parts. It is advisable to wear gloves while mixing and pouring as well.
When pouring the plaster into the cast, go slow to avoid leaving air bubbles anywhere. Shaking the mold a little will also release any air bubbles that may have got trapped inside. Now wait for it to cure before demolding the plaster casting gently.
For the cleanup part, it is better to rinse out the mixing bucket and mixers before the plaster can set. But don't wash it down a drain as that will clog as well. Instead, pour it into a plastic bag and throw it away after it sets.