China model horses are slipcast, which means they are made by pouring liquid clay into a plaster mold. Once the clay inside the mold has time to set up, the excess slip is poured back out. That is why china horses are hollow like a chocolate Easter bunny.
There are three types of slip widely available in the United States: earthenware, stoneware and mid-range porcelain. A fourth type, bone china, is traditional in the United Kingdom but isn't available in the States.
Earthenware
This is the clay associated with American art pottery. Hagen-Renaker pieces are made of earthenware slip. Earthenware slip fires at Cone 04.
Stoneware
This is the type of clay common in “clay studio” settings. It is stronger than earthenware, but tends to be more gritty (less smooth) and has a higher rate of shrinkage. White stonewares are typically closer to cream than the warm white found in earthenware. Stoneware slip fires at Cone 5 or 6.
Mid-range porcelain
This type of slip is commonly used for dolls. Once fired, it is extremely durable, but in its greenware form it is extremely fragile and prone to crumbling. Unlike the previous two clays, it can sag during firing unless propped. It does come in a wide range of colors, including a true neutral white. It fires at Cone 6.
Slip colors
The most common color for slip is white, but the exact shade varies. Bone china is usually a bright, cool white. Next to the other clays, it can have a bluish cast. Earthenware is a warm white, ranging from winter white to ivory depending on the formula. Stoneware is warmer still, with many "white" stoneware slips coming out a color closer to cream than white. Mid-range porcelain is a cooler white, though the undertones of some white porcelains can have a grayish cast compared to the brighter, bluer bone china. In the photo at the top of this post, the Xavier (facing, far left) is bone china. Next to him are two Peritia medallions (shown from the back), earthenware and stoneware respectively. In front of those is an Inspire tile (facing) in mid-range porcelain.
Slip can be found in other colors. Earthenware is also produced in terra cotta, which looks much like the acrylic paint of the same name. Stoneware is commonly produced in a darker cream with speckles. Because it is most often used in doll production, porcelain is made in a wide range of skin tones. Most ceramic horses are produced in white clay, but some manufacturers have experimented with colored slip. For example, the Pour Horse Hadrian was made with brown-tinted earthenware.
More about slip
It is important to note that slip is more than just watered-down clay. Precise ratios of chemicals, known as deflocculants, are added that keep the clay in suspension. For that reason, adding water to moist clay will not create usable slip for casting.
Slip that is firm enough to be removed from a mold is referred to as leather-hard. Leather-hard clay will break when bent, rather than deform. Clay that has dried, but has not yet been fired, is called greenware. Once it has been fired, but not yet decorated, it is called bisqueware or just bisque.
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| An art-glazed stoneware Peritia placed back-to-back with an earthenware bisque, showing the difference between the shrinkage of the two clays. |
Slip shrinks as it dries, and then again when it is fired. Different slips will have their own rate of shrinkage, but generally earthenware slip has a lower shrinkage rate than stoneware or porcelain. For example, the earthenware slip that I use has a shrinkage rate of 5%, while the stoneware has a rate of 13%.
Practical considerations
Each type of clay has its own strengths and limitations. For someone just learning to make ceramic horses, my choice is earthenware. It is forgiving of mistakes. It doesn't require propping during firing. I also make a lot of horses with white patterns, and I like the natural look of the slightly warmer whites. For my own editions, I use a slip based on the old Hagen-Renaker formula. For medallions, though, my choice is Standard Clay's Artist White. I find it particularly sturdy in the greenware stage, which makes the castings more beginner-friendly.
When I want to use stoneware glazes (more on those in the next post), I use white stoneware slip. My favorite is Laguna 500L, though it can be hard to find in liquid form. I prefer not to mix dry ingredients. Liquid clay is messy enough, and there is enough dust mitigation in pottery without intentionally bringing in more.
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