Introduction of Coloring Pigments
With the introduction of the second group comes an added interest and difficulty, that of the introduction of color. Pigments that will withstand the application of heat are suggested at different points.
Inlay
4. This process consists of removing certain areas from the clay body to the depth of one-eighth inch and filling in the depression with tinted clay. Tints formed by the addition of ten per cent or less of burnt umber or yellow ochre to the modeling clay will give interesting effects. [Figures 284], [285], [320], and [321] show forms which may be developed by this process.
Sgraffito, an Italian process, is more difficult than inlaying, but the effect is similar. A thin layer of colored clay is placed over the natural clay body, and the design is developed by cutting away this colored coating in places, thus exposing the natural clay body. [Figure 306]. There are variations of this plan that may be attempted by the advanced designer.
Slip Painting
5. Slip is clay mixed with water to the consistency of cream. For slip painting this mixture is thoroughly mixed with not more than ten per cent of coloring pigment as represented by the underglaze colors of the ceramist. This thick, creamy, colored slip is then painted on the surface of the clay body while damp, much as the artist would apply oil colors. The ware, when thoroughly dried, is glazed and fired, which produces the effect shown in [Figures 290], [291], and [327]. The color range is large; almost any color may be used with the exception of reds and strong yellows. A colorless transparent glaze should be used over beginner's slip painting.
Colored Glazes
6. This process refers to the direct introduction of the colored pigment into the glaze. By varying the glaze formula we may have a clear, transparent, or glossy glaze similar to [Figure 317], a dull surfaced opaque effect, termed a matt glaze, [Figure 332]; or a glossy but opaque faience glaze similar to the blue and white Dutch tiles. There are other forms such as the crystalline and "reduced" glazes, but these as a rule are far beyond the ability of the beginning craftsman in ceramics.