How to Make a Slip Cast Mold

Written by jennifer meyer
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How to Make a Slip Cast Mold
Most manufactured ceramics are made using slip moulds. (ceramics image by Andrey Rakhmatullin from Fotolia.com)

Sometimes a potter finds that it makes more sense to create detail using a mould than it does to handsculpt ornaments individually. For these cases, potters use slip moulds. Slip is a viscous solution of water and clay that you pour into a mould. Over time it dries, just like regular clay, but it takes on every detail of the mould. Most slip moulds are slightly larger than they need to be because clay shrinks as it dries.

Skill level:
Moderately Easy

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Things you need

  • Sink
  • Bucket
  • Gloves
  • Face mask
  • Prototype
  • Newspaper
  • Pottery plaster
  • Liquid soap
  • Paper towels

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Instructions

  1. 1

    Lay newspaper across your work surface and don your gloves and face mask. Rub the surface of your prototype down with a thin veneer of liquid soap. The soap will keep your mould from sticking to your prototype ornament.

  2. 2

    Pour pottery plaster into a bucket. Pottery plaster comes as a white powder in plastic bags or tubs. Add enough of it to completely cover your prototype.

  3. 3

    Carry the bucket over to a sink and add water. Stir the water and plaster with your gloved fingers. Stop adding water when the plaster has the consistency of mud. Stir it for an extra 10 seconds to make sure that there are no lingering bits of powder.

  4. 4

    Pour the plaster sludge over your prototype. Guide it with your finger so that it fills every crack. Make sure that the pottery plaster is at least 1 inch thick at any given point.

  5. 5

    Let the plaster harden overnight.

  6. 6

    Turn the mould over, peeling it away from the newspaper, and gently work the prototype out of the mould. Go over the mould with a damp paper towel to clean off any soap residue.

  7. 7

    Let the mould fully dry for a week before you use it to cast your slip.

Tips and warnings

  • When casting with your slip mould, talc powder can be used as a mould release.
  • Pottery plaster is not suitable for inflexible ornaments with large undercuts as it cannot bend after it hardens. Do not use pottery plaster on any prototype with appendages that would be difficult to remove from a solid mould.

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