engobes part one

engobes...colored slip article part one
ArticlesEngobesEngobes can be defined as liquid clay slips of varying compositions which are applied to the surface of a clay object, e.g. a pot. The purpose of the engobe can be as different as the varied forms it comes in: to give color to a piece; to improve the surface texture; to provide a ground to do further decoration on; to add textures.Engobes can be applied to wet clay surfaces, leather-hard ware, greenware and even bisqued wares. In each case the engobe's shrinkage rate should match that of the clay underneath, otherwise cracking (when the engobe shrinks more than the clay underneath) or shivering (when the clay underneath shrinks more than the engobe on top) can occur. While there are some basic engobe recipes around, The Potter's Complete Book of Clay and Glazes by James Chappel has a range of engobe recipes for diferent grades of moisture content and firing ranges from cone 10 up to cone 11 (for more information on cones, see cone chart).Here is a simple cone 6-11 engobe you can try out on leatherhard clay (Rhodes, Clay & Glazes for the Potter), but be sure to do some tests first, before using it on any 'important' stuff:Kaolin 25Ball clay 25Potash feldspar 20Flint (Silica) 20Zircopax 5Borax 5If applying the above to greenware or bisque, experiment by substituting increasing amounts of calcined kaolin.Application techniques for engobes also greatly vary. They range from dipping to brushing and spraying and even slip-trailing, However, in contrast to applying glazes to bisque ware, it pays to be careful when applying engobes to greenware, as the clay can soften and deform, e.g. if a pot is dipped too long. During application, wax or latex can be applied as a resist. Once the engobe has hardened, designs can be scratched in, revealing the clay body underneath.Next Page > Engobe Color Chart > 2More Articles© Ceramics Today