Slip is composed of a number of raw materials, primarily three. Kaolin, which is a white primary clay that has minimal impurities like iron and titanium. Kaolin is mostly mined to be used as a filler in magazine paper to make it glossy. The kaolin we use in porcelain is white and translucent. In order to make the kaolin form a glass, we add silica which is also flint or glass and something called a flux to make these two melt. I like to describe the combination of the three as a glass body with a kaolin skeleton. Therefore, the more you make the materials melt the more translucent it becomes. However, if you make them melt too much they will not hold their form. The last thing that is added to these raw materials to make the porcelain workable is water. We use distilled water to limit the amount of minerals such as calcium. What makes porcelain set apart from other clays you may know such as stoneware or earthenware, is that it is chemically more sound and lacks impurities that would potentially diminish the strength.
The way we work with our porcelain is by making it into a liquid. We do that by adding something called a deflocculant. The deflocculant ultimately causes particles to suspend. This suspension allows less water to be used in the clay and essentially makes water wetter. Our porcelain has significantly less water than throwing clay. We use slip for a couple reasons. Its one of the easiest ways to work with porcelain.
What we love about slipcasting is that it allows us to explore forms that are off the wheel so that we can expand the library of shapes beyond what we could on the wheel. Also, there’s nothing sexier than a big vat of liquid porcelain.