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How To Use A Slump Mold For Pottery

What is a slump mold?

Slump molds are essentially concave shapes that work in a similar fashion to any other molds. With slump molds, the clay is draped over the surface of the mold and ‘slumps’ into the shape created.

With slump molds, the inside surface of a pot is exposed, while the outer face is in contact with the mold. This enables you to add embellishment to the inside of your project and also decorative features such as lips.


How do I use a slump mold?

Using a slump mold is a fairly simple process. Use a simple slab of clay that has been pre rolled to around ¼ inch thick, then the clay is draped across the surface of the mold and pressed or knocked into the shape.

A wooden rib can then be used to smooth any blemishes and a knife can be used to trim away any excess clay. You should use a fairly plastic clay with any suitable firing temperature. You should use a clay with a moderate grog content as slump molds lack sharp details that would be worn away by clays with a high grog content.

The clay is then left to dry at room temperature and any embellishments, such as a decorative lip may be added to the clay before being removed from the mold. Once dry, the clay is ready for firing.

brown pot


Why use a slump mold?

Slump molds are effective at producing standardized pieces of pottery, which is particularly useful if you have a pottery business that sells uniform pieces. The fact that there are many ways to create these molds means that you can get creative without the expense.

Slump molds also enable you to create perfect bowl-like shapes, which are not always easy to create on a pottery wheel.


What to use for a slump mold and how to make them

There’s no real need to make a massive investment into a slump mold. In fact, many slump molds can be crafted or made from existing materials. A slump mold can be made from an old piece of earthenware, or plaster bowl that achieves the shape that you wish. In addition, there are a number of molds that can be crafted from various materials.


Slump molds made with plaster

Plaster is a great material through which to craft your own slump mold. The consideration however is that it must be ceramic grade, and you need to be careful with the chemicals that you’re using. Once made, they can be reused again and again, which is particularly useful if you are mass producing the same item.

You will need the following materials:

  • Ceramic-grade pottery plaster
  • A NIOSH mask to prevent harmful plaster dust from getting into your lungs
  • Water
  • A bucket 
  • The objects you’re building the mold from. Choose something flexible so that it’s easy to remove
  • A spray bottle of vinegar
  • A scooper
  • Something to stir the plaster
  • A scale

The instructions for making your own slump mold from plaster are as follows:

  • Take a pound of water and measure 1.5 pounds of plaster mix
  • Stir, trying to get rid of as many lumps as you can
  • Tap the mold on a sturdy surface to remove bubbles
  • If there are bubbles on the mold itself, spray lightly with vinegar 
  • Wait at least 3-4 hours before you take it out
  • Gently tap the mold out of your plastic
  • Gently sand or rub out any imperfections


Making a slump mold on a potter's wheel

First, work your clay to get it centered, creating a flattened pancake shape. Then, start driving the clay out more and more and from there, starting to create a flat circular piece.

Once you are happy with your shape and size, you can then start opening up the inside, start to pinch and move outwards. Once you have the walls built, you can then start to line both the inside and the outside more.

Thin out the walls a little bit on the inside of your mold, but keep them thicker than your normal bowl so that they create a sturdy mold.

Clean up the inside with some wooden tools, helping to define the shape. Finally let it sit to harden and then fire using an electric powered kiln.


Making a slump mold from cardboard

As mentioned previously, you can make a slump mold out of virtually anything, so long as it is robust and you are only using it in the pre-firing stage. For a cardboard slump mold, you will need a strong cardboard box, a sharp knife and your block of clay.

Draw your desired shape onto the box and cut around the shape with a sharp knife. Next, place a rolled out slab of clay over the cut-out opening. Carefully pick up the box and drop it onto the table from about 6 inches, the clay should slump slightly into the hole. Repeat the process until the clay has reached the depth you want.

Finally, trim the excess clay and turn out the completed form onto a board to dry. Once the clay has dried you will then be able to fire the clay on your desired programme - preferably using an electric kiln.


What do I do once my ceramic piece has been created using a slump mold?

Once you have created your piece and you are happy with its shape and embellishments, an easily controlled kiln is essential for finishing your piece and hardening it for practical use. Temperature control plays a crucial part in the success of your outcome. Electric kilns can modify and manage the temperature at the right heat and duration and so the firing process can be well controlled.

At Soul Ceramics, we have a range of high quality electric kilns which can accommodate small or large projects. They can allow you to finalize your slump mold item and can be easily programmed to achieve the best finished project.

If you would like to know more about our range of kilns or you are looking to invest in a kiln for a hobby or as part of a business, please do not hesitate to contact us and we’ll be happy to advise you on the most suited kiln for your project.


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