Silt Casting and Slip Casting
We will hopefully be doing some Slip Casting to make hollow resonant forms that we can use for our instruments.
What is Slip?
Slip is clay particles suspended in water.
What is Slip Casting?
Slip Casting is a procees in which slip is poured into a porous mold, often plaster. Over time, water seeps out of the slip through the mold, allowing the clay to build up on the interior surface of the mold. Once the desired thickness has been achived, the mold is drained of excess slip (to be recycled) and opened. The resulting object is a hollow form whose exterior shape resembles the interior of the mold. Plaster molds can be re-used, making it easy to create identical complex hollow forms again and again from one single mold.
The video below is a great visual representation of this process and why ceramic artists might choose to use it:
What is Silt?
Silt is made of of very fine sand particles, making it very even-textured and able to compact. Silt is found all over the world in most soil samples, often near riverbeds and other places where particles are moving and rubbing against eachother frequently. See the Soil Shake Test page to test if there is silt near you!
What is Silt Casting?
In silt casting, we use silty soil to make our mold instead of plaster, casting directly into the earth! This produces a much more organic and textured form, without losing any of it’s resonance and strength. Once removed from the Silt, the cast clay forms can also be carved before firing. Silt molds can be used multiple times, but the texture increases every time, each cast clay form is unique!
This past fall Morgan had the opportunity to learn silt casting at Arcosanti, an experimental architecture and ecology foundation in Arizona that specializes in cast bronze and clay bells. Arcosanti’s bells are made using the traditional silt-casting method and are famous all over the world.
Some of the chime components for the Window Instruments could be made by casting custom shapes from molten Aluminum. Aluminum forms ring nicely when struck.
That’s right! There are safe and accessible ways to work with molten aluminum at Camp. With the right safety gear and training process, we will be able to cast aluminum into sand molds.
Green Sand can be temporarily formed into molds, cast (poured into) with molten aluminum, and then reused for other molds. The Green Sand mold can withstand the heat of the molten aluminum - 1200 degrees Fahrenheit!
They call it Green Sand because it’s a mixture of fine sand, bentonite clay and water - not unlike our Cob mixture! In the proper ratio, the clay in the sand makes it ‘sticky’ so it can stay molded around your original shape.
We’ll be using a technique called ‘Lost-Foam’. An object is made out of foam, then packed carefully into a Green Sand Mold. Pour Sprues and Vents are added to the mold, and then the molten aluminum is poured into the mold.
This foam shape... ... turns into this!
The temperature of the molten aluminum (1200 degrees F) is hot enough to instantly melt and evaporate the foam object. After the mold has cooled, the aluminum is dug out from the sand.
Aluminum has good tonal qualities when struck with a mallet.
And... an amazing video of the entire process. We’ll be using safety gear and moving a bit slower! ... and our original shape will stay encased in the sand.