For many craftsmen and ceramists, knowing how to make a plaster mold for ceramics is of vital importance when making the pieces you need since they can be applied to any object and are easy to make. In this interesting article, you will learn how to make these molds in a simple and well-explained way. Keep reading!
What is a plaster cast?
When we refer to a plaster mold, we are talking about a multifunctional and easy-to-use mold that allows the production of all kinds of pieces through serial work.
It is used to make pieces through levigation molding, which consists of dividing the grains of dough by diluting them in water under a decanting system that allows the dough to be purified. This process generates a mixture called slip, which is nothing more than the substance that remains at the bottom of the container used to decant the plaster. It is even used to make ornamental pieces or as glue on already made plaster pieces.
Making molds with plaster was not widely used by ancient artisans, since for them it was to detract from the value of handcrafted pieces. However, at present, the development of these molds has been used to advance in the manufacture of a large number of pieces.
What is plaster?
Before starting to make a plaster mold, you need to learn a little about this raw material and its uses in the pottery industry.
Gypsum is a moldable material, it is a hydraulic binder, used to make different molds through water casting, which gives them a certain porosity.
The durability of a plaster mold will be proportional to the quality of the raw material used to make the mold and the care in its manufacturing process.
Strength and durability of a plaster mold
The resistance of the plaster base to make molds is based on several elements that we will define below:
Gypsum/water ratio
The resistance and durability of the plaster molds increase while the gypsum/water ratio is increased, always taking into account not to impair the malleability of the preparation.
Mixing time
The longer the mixing and blending time of the preparation, the greater the resistance. This must be done without overdoing it since if the mixture is over-stirred, the dihydrate crystals that have formed can break, deteriorating the crystalline framework, which would result in a less durable mold.
Air bubbles trapped in the mix
The greater the amount of air trapped, the greater the number of bubbles and the greater the risk factor for the mold to break or crack. This can be avoided by gently and continuously stirring the mixture, and adding the dusted plaster little by little.
Additives
When setting accelerators or retardants, etc., are added to the mixture of plaster and water, the hydration of the same and its malleability can be modified, which will prevent the creation of a resistant and durable mold.
How to make a plaster mold for ceramics Step by step to make a plaster or plaster cast
Next, we will describe the step by step to make a two-piece plaster mold. The first thing we need is the appropriate materials for the elaboration, which are:
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Now yes, once we have the materials we get down to work.
Start making plaster mold for ceramics
The part to be used must be clean, without defects, and well polished. Vaseline is spread all over the object, so that it is well covered, with a not too thick layer.
The bottom of the box that will be used for casting can be covered with plasticine so that, when placing the piece for the mold, it remains fixed. The amount of plasticine must be enough for the chosen piece to sink exactly halfway, exposing the other half of it. Based on this, the result will be a two-part plaster cast.
The plaster mix is made according to the instructions we have, which may vary depending on the brand of it. It is recommended that its consistency is pasty and does not contain bubbles. To do this, you can hit the bowl where the mixture is prepared against the work surface until there are no bubbles.
The plaster preparation is emptied into the casting mold until the piece is completely covered. It is necessary to allow the plaster to dry completely before removing the piece from the mold.
Then the same steps will be repeated, on the other side of the piece.
When removing the mold already made and completely dry, we proceed to gently sand the rough or lumpy sides.
How to make plaster objects
The plaster is a material that lends itself to all kinds of repairs and DIY jobs at home, but it can also be used to make various crafts, and actually build even decorative objects. We already know how to make a plaster mold for ceramics. Let’s see then a step guide in which we explain how to make plaster objects.
Gypsum is a very flexible material that is obtained by dehydration by pulverizing the gypsum stone. It is generally sold in 20 or 40 kg bags, or in smaller 1 kg bags for small jobs, which are what we are going to carry out for all kinds of crafts so we are going to offer you a guide that will help you make objects.
Materials you’ll need to make plaster objects
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Step to make objects with plaster
Step 1 to 5 making plaster mold for ceramics
- We will start by preparing the plaster mixture. So you should mix the plaster powder with clean water. The proportions of the dough will vary according to the type of work to be done but to mold in a mold, the plaster paste must be quite liquid.
- To make the dough you must pour water into a perfectly clean plastic container. Then add the chalk powder.
- Let the plaster absorb the water for about 15 seconds, then begin mixing the batter with a spatula or small trowel.
- If the container is concave, we recommend using a paddle with a rounded tip, but if the container has a flat bottom, we recommend using a square paddle or spatula.
- Plastic or wooden spatulas can also be used to knead the plaster.
Step 6 to 10 make a plaster mold for ceramics
- Make sure to mix well so there are no lumps, and to get a dough that is smooth and thin. A good mass is an essential condition to face the next part of the job, whatever it may be.
- Once the mixture is done and well kneaded, you have to use it quickly because the setting of the plaster will continue and it is not possible to add water to dilute the mixture once it has started to harden.
- The plaster can be colored with acrylic colors once it has hardened, however, we can also do a color mixture if we want to obtain a particular color when we make the dough. For this, you must add the powder pigments to the mixture of water and plaster powder.
- On the other hand, you can also perfume the mass with scented essences whose aroma will remain imprisoned in the plaster and will remain when the plaster is hardened.
- To make decorative plaster objects, you will almost always have to resort to special silicone molds, into which you will have to pour the mass that you have made with the plaster. To obtain three-dimensional objects it is necessary to use bivalve molds. Bivalve molds make it possible to obtain two parts, front and back, of an object, parts that must later be joined.
Step 11 to 15
- The part of filling the molds is perhaps the most difficult phase and must be done carefully if we want to obtain an object without imperfections.
- The procedure must be carried out with some speed and, at the same time, with precision.
- To do this, we pour a first part of the dough into the mold and with the help of a spatula, we make sure that the dough is smooth inside the mold, and no bubbles are formed.
- Then we just fill the mold to the edge and then we remove the excess with the spatula so that even the back of the created object is perfectly smooth.
- Once dry, the plaster will have acquired the same shape as the mold and thanks to the flexibility of the silicone it can be easily removed.
Conclusion
And ready! As you can see, making a plaster cast is not complicated if you follow this step-by-step guide. And if you want to know more about plaster molds for ceramics, continue reading us. I wish that how to make a plaster mold for ceramics will helping you.
