Slips, engobes and underglazes are a lot of fun to use for ceramic decoration and there are endless ways to use them.
Today, Robin Hopper explains how you can achieve many different types of surface decorations and patterns in a short period of time using only a simple slip trailer. The post is an excerpt from Making Marks: Decorating the Ceramic Surface, a must for every potter’s ceramic library. – Jennifer Harnetty, editor.
Slips and Engobes
Slips are predominantly liquefied clay; they usually are applied on wet to dry greenware. Engobes usually have a lower clay content and also can be used on bisque-fired ware. The word slip generally is used to describe any clay in liquid form. All slips and engobes can be colored with oxides, carbonates and stains. Sometimes very crusty surfaces can be made by applying slips and engobes over the fired glaze surface and then refiring.
Casting slips give extremely good properties for use as a drawing medium in a fine-to-medium aperture trailer. To produce slips for casting into plaster molds, the ingredients for slip are mixed with water to which 1 percent to 2 percent of a deflocculant, such as sodium carbonate (soda ash) and/or sodium silicate, has been added. Since there is much less water in the deflocculated slip, it will leave a crisp, raised line drawing when applied to leather-hard surfaces. To remove sharp points or develop a low relief, raised line slip drawings can be flattened slightly by rolling the surface with a small rubber-coated roller or printmaker’s brayer.
The word engobe is used most often in North America and describes a wider range of uses in the development of the decorative surface. Underglaze is basically the same thing, and it can be colored with any colorant or stain. Many commercially made underglaze products are available, offering a wide range of color potential. They are applied easily by brush or spray. Whereas the simple liquefied slip commonly is used to coat greenware, an engobe can be formulated for use at any stage, including over bisque-fired ware. Engobes also often are used without a covering glaze, giving a wider potential for experimentation with the surface. An engobe or underglaze is more like a glaze in structure and may contain very little plastic clay.
|Raw Material||Cone 04-3||Cone 4-6||Cone 6-10|
|Calcium Borate (or Frit 3110)||15||10||0|