Gypsum casting

Gypsum is a useful material in art for casting gypsum into a mold and creating a gypsum mold for casting from another material. Although the process of preparing gypsum for casting is simple and quick, familiarity with the material and work skills is required as the gypsum dries quickly and the time span for the work is very short. 


Facts and properties of gypsum

  • Gypsum is a very soft mineral composed of calcium and sulfate. It is a natural substance formed as a precipitate when water evaporates in lagoons or closed lakes. There is also synthetic gypsum, called plastic gypsum. Plastic plaster is used in medicine, construction and art.
  • In the art gypsum is used as a material for the production of a mold or as a casting for an existing mold. Gypsum preparation requires only water and work skill. Gypsum begins to dry out and harden after about 15 minutes of dissolving in water, so it is important to work fast and not procrastinate.
  • When the plaster is poured into a ready-made mold it gets its shape. The gypsum mixture dissolved in water flows and fills each perforation in the mold. Thanks to this feature you can be precise in small details.
  • Apart from gypsum that comes in powder form, there are also gypsum bandages in the Galilee. The plaster is glued to a delicate and special felt, when wet it becomes flexible and adheres to different materials and the body, so you can create sculptures according to your wishes. When it dries it becomes hard and can be painted.
  • Gypsum is a relatively inexpensive, accessible and easy-to-use material, making it very popular for creation for children. 

Uses with gypsum in art

  • One of the uses is Create a template for a clay sculpture. It will be possible to pour liquid clay into it and thus duplicate the statue. When creating a mold, cast plaster on a clay sculpture. When the mold dries, the clay is extracted and an empty mold is left. Liquid clay can be poured into it, creating copies of the original sculpture.
  • Another use is to create a relief with the help Ready-made template. The prepared gypsum mixture can be poured into a plastic mold or a ready-made silicone mold. A ceramic clay mold can be made in a disposable plate. What you create will stand out will be concave in relief. Conversely, whatever you create concave will stand out. Do not dry the clay used for the gypsum mold. Otherwise it is impossible to remove the plaster relief from the mold.

Equipment and materials needed to make gypsum for casting:

1. Gypsum powder for casting
2. Plastic box / bowl
3. water
4. Spatula for mixing
5. Casting molds
6. Pattern Supporters
7. Sandpaper


Step-by-step instructions for making gypsum casting

Please note: the plaster dries and hardens within half an hour. It is not possible to prepare gypsum in advance and save it for casting afterwards. Act consistently and quickly without distractions.

Depending on the desired amount of gypsum (in this example we used 1 kg of gypsum for 1 molds) Prepare water in a soft plastic or rubber container, at a rate of 1 ml of water per 1 gram of gypsum (1 kg of gypsum - 1 liter of water). The water in the vessel should fill no more than one-third of the vessel's capacity. Gradually, pour the gypsum powder into the water, until the gypsum absorbs all the water. 

2. Mix the wet gypsum well until a uniform, lump-free mixture is obtained. Mix with the spatula back and forth until the texture of the liquid gypsum is similar to the texture of raw tahini.

3. Knock a little with the container on the table that all the air bubbles have come out - and the plaster is ready to pour.

Preparation of gypsum for casting

4. Place the gypsum molds inside mold supports so that they are stable for casting. For template supporters it is possible to use any deep tool of the appropriate size to stabilize the template. If you pour gypsum into a clay mold that you made yourself - there is no need for a support.

5. Gently pour the gypsum mixture into the molds until the molds are full.

Preparation of gypsum for casting

6. Straighten the plaster with a spatula.

Preparation of gypsum for casting
Preparation of gypsum for casting

7. Shake the molds slightly and gently so that more air bubbles come out.

8. Allow the plaster to dry and harden. 

Preparation of gypsum for casting

9. The plaster will first begin to heat up and gradually cool down. While the plaster is still hot, carefully remove the plaster reliefs from the mold.

Preparation of gypsum for casting

10.  Gently remove the plaster from the edges of the relief. The edges of the gypsum relief can be sanded with sandpaper.

If holes are formed as a result of air bubbles, they can be filled with Splashing cracks. Do not fill the holes with liquid gypsum as it will just fall off over time.

Preparation of gypsum for casting

11.  Leave the reliefs to dry completely. It is recommended to put in the open air with direct sun on a ventilated surface (any mesh).

Preparation of gypsum for casting

12. Now the gypsum casting is ready for painting. It is recommended to paint the plaster reliefs with gouache or acrylic paints and decorate it with various ornaments with the help of plastic glue: for example, glitter, sequins, moving eyes and more. If you want to leave the relief in white, it is recommended to cover with white gouache and plastic glue in a 1: 1 ratio in order to preserve the work for a long time. This way you can easily wipe off the dirt and dust that accumulates. In addition, to allow the gypsum reliefs to hang on the wall, stick hanging triangles on the back.

Preparation of gypsum for casting

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