Not so long ago, I wanted to learn how to slip cast porcelain. Lucky for me Nathan Tucker of Powder Studio, a local slip casting studio focused primarily on creating porcelain lighting, was happy to teach me.
I wanted to learn the beginning to end process, the traditional method of slip casting, which has been around for centuries. I wanted to make my own mold from scratch, literally hand carving the shape to be cast and replicated. There are easier ways to get the same result, like using pre-made plastic or rubber forms and casting those, but you have more control when making it yourself. And plus I was learning the process.
I chose a heart shape, as I thought it would be relatively easy and a little more dimensional than just a round ball shape.
I quickly learned hearts are not as easy as they look. Not only do you have to carve front and back to look relatively the same, but the sides and top bottom have to flow together optically as well. I wasn’t used to thinking in 3D. Nathan finally helped me round out the heart form. This is what I would create a mold from (see below photograph).
The next step was creating a mold to cast with. Once the heart form was completed, I smoothed the surface with fine sandpaper and and several coatings of Murphy Oil. Notice the difference in heart surface between the above and below pictures. Murphy Oil seals the heart and creates a smooth surface for the mold. I then surround the heart with coils of clay to build formwork framed with cottle boards.
From there Nathan helped me pour the plaster mold and let it set overnight. Once it’s dried the next day, I removed the formwork and flipped it to pour the other side. These will be the front and back sides of the mold from which to make slip castings of the heart.
Here is what the final mold looks like (see below), cast from the original heart. Using this mold, I can now cast exact replicas of the same heart shape in porcelain. This is the purpose of slip casting.
Next comes preparing the slip and pouring into the mold to create my first porcelain heart! Slip is basically a mixture of watered down clay and some extra compounds to control the viscosity related to the water content of the slip. Knowledge of chemistry (and cooking, I found out!) goes a long way when formulating a porcelain slip.
In this case, watered down porcelain. For slip casting, generally the slip should be mixed at least 20 minutes prior to using to get it smooth enough to pour evenly into the mold.
Pouring the slip is easier with two people. Once the mold is filled, the slip is then poured back out of the mold after a certain amount of time. How long you wait determines how thick the walls of the cast will be. When you cast a mold, you are coating the walls of the mold. The center will be hollow.
Then you wait between 2 – 24 hours to de-mold, depending on factors such as scale, wall thickness, ambient humidity and temperature.
Finally, open the mold to reveal the cast porcelain heart! The heart is hollow with a hole underneath where the slip was poured to create the cast (the “pour spout”). After the heart comes out of the mold it must dry out to be sanded down, smoothing away any rough edges. This is called the greenware stage before firing.
Here are several hearts cast from the same mold in various states of drying before the first kiln firing at cone 05.
This first partial firing is called the bisque firing, which prepares the porcelain to be glazed by increasing durability while maintaining the porcelain’s porosity (ability to “soak in” the glazes). Below are several sanded hearts that have come out of the kiln after their first firing and are waiting to be glazed.
I wanted to do some glaze testing to see the look of the glazes first. Below are a few hearts prepped with different whites, matte and satin finishes and a close up of the different finishes after firing.
I decided on a satin matte white for the remaining hearts. Below is how they look after firing.
The final stage was adding decals over the satin glaze. Decals can be made from both vector or pixel artwork. They can be anything from a scribble to highly precise line art, or a photograph. They are somewhat expensive to create and you have to have them made. After uploading your artwork to a decal maker, within a week they send you your files on clear sheets of film with a backing.
To apply a decal, soak for 30 seconds in warm water. Remove the backing and place the decal directly on the object where you would like it. Gently rub down with a squeegee or sponge to get all the air bubbles out. Once you’ve placed your decals, let it sit overnight to dry out. You don’t want to fire with wet decals.
The third round of firing for decals is at cone 16. For a fourth firing, you can add metallic lusters at cone 22, as an option.
That was my slip casting experience! As you can see there are many steps involved, but with practice and a system in place, you can pretty much create whatever you like.