Baked Cast Slate

Experiment

Casting

Material

Minerals and stone

Craft

Ceramics and pottery-making

General Technique

Combining

Specific Technique

Simple process of combining materials, baking them in an oven, and letting them dry. Borrowed aspects from ceramics / slip casting process.

Properties & Qualities

Application

Furnishing Lighting Sculpture Other

Colour

Grey

Sample Information

Date of creation

January, 2021

Dimensions

110mm x 60mm x 30mm

Weight

70g

Culture & Context

I used slate from a local quarry in Valentia Island, Ireland.

Valentia slate has many notable historic applications in and outside of Ireland, and holds significance when doing a deep dive into traditional Irish materials, and Irish material culture. 

This material was an attempt to work with slate in a new and contemporary way, bringing a breath of fresh air to how designers can work with locally sourced stone.

Process & Production

Wear a dust mask while handing slate dust, wear gloves when handling sodium silicate.

Recipe Details

Air dry cast slate:

  • Collect slate silt.
  • Rinse silt with clean water.
  • Dry silt to remove moisture, preferably in an oven, until it is a dry powder.
  • Sift powder to break up clumps, achieve uniform consistency.
  • Measurements by weight: 70% slate, 15% water, 15% sodium silicate. (experimentation + samples is recommended)
  • Combine water and sodium silicate, mix well. 
  • Combine the diluted sodium silicate with the slate powder.
  • Mix thoroughly to remove clumps. 
  • Add mix to non-porous mold. (porous molds will extract the water and sodium silicate from mixture and intervene with bonding process, resulting in a crumbly product)
  • Put in oven and bake at 150-180C. Time in oven depends on casted piece. Baking the mixture does a few things. The goal is to get the water in the mixture to evaporate into a gas and expand, creating various air pockets. The mixture will “rise” similarly to a cake. Likewise, air pockets will also collapse slightly after being taken out of the oven. 
  • Let dry for at least 24hrs. 
  • Your cast piece can now be trimmed using a saw to remove uneven surfaces and expose the even-toned, “cake-y” slate. 
  • Let dry until solid. (Drying time depends on the size of casted piece, drying time could take up to 2 weeks or more for larger pieces. CO2 improves the hardening process, and accelerates drying time. Otherwise, use a drybox, with a fan and dehumidifier. The goal is to remove all the water from the solution, and allow the sodium silicate to bond all the slate together)

Credits

Craft Maker

Nicolas Wijnstekers

Library Contributor

National College of Art & Design Ireland

Photographer

Nicolas Wijnstekers

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