|Since the cost of an accurate gram scale can be an obstacle, an economical way to get started is with a volumetric recipe. Such a recipe requires the ingredients to be measured in cups (or teaspoons, tablespoons or buckets). While less exact than weighing ingredients to the tenth of a gram, this type of recipe can yield fine results and lends itself to experimentation. A good place to start might be with the very basic recipe of 2 parts colemanite (Gerstley borate, or commercial Gerstley borate substitutes) to 1 part Kona F-4 feldspar to 1 part silica. This becomes a clear glaze at Cone 5-6, but because of the high level of boron in the colemanite, it’s rather milky. It’s easy to add various coloring oxides or opacifiers in teaspoons and tablespoons to achieve a wide range of colors from this simple recipe|
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Other experiments might be to substitute various feldspars for the Kona F-4, or to try simple additions of other common glaze ingredients. Keeping a supply of test tiles handy-or even pieces of broken bisque-ware-means that any time you get the urge to mix up a quick experimental glaze, you’ll have something to try it on. Learning about glazes this way undoubtedly produces some strange results, as well as some successful surprises. As long as you keep good records, you’ll gradually add to your store of knowledge, and develop familiarity with the many glaze materials in a fun and nonstressful way. While such experimentation isn’t likely to satisfy any potter forever, it offers an easy way to play with mixing and using glazes at home without requiring a large investment in equipment and materials or a great deal of space.
Volumetric Glaze Recipe The following recipe was developed from the basic recipe given, and modified to reduce the milkiness and add the extra calcium required by many commercial stains. The nice thing about this glaze recipe is that not only is it easy to mix, but with stains you can mix up several different colors of glaze, using only five basic ingredients. The stains can also be mixed into the clay body or into engobes and painted onto the pot before bisque firing. This glaze can then be applied as a clear base. It can also be applied to a pot and decorated with stains mixed with a little glaze.
CAUTION: When handling dry glaze ingredients, always wear a NIOSH-approved respirator.
Add stain in amounts between 1 and 2 parts. The pink and red stains work nicely in a ratio of 8 parts base mix to 1 part stain. To test several colors, mix up a batch using large units such as cups. Mix the dry ingredients together thoroughly by shaking them in a large sealable bag or in a bucket with a tight lid; allow to settle before opening. Use 2 tablespoons of stain to each standard (8-ounce) cup of glaze mix.