- THE MAGAZINE
For an increasing number of hobby and studio potters, commercial glaze products are providing a solution to the time crunch and quality problems that are often encountered when making glazes from scratch. Yes, I know...part of your creative adventure includes creating your own glaze products. But what if you could have a wide range of underglazes, glazes and overglazes, without the time and mess of making them yourself, and still have the feeling of personal accomplishment when you open the kiln?
I understand the desire to "create from scratch." I love to cook-really cook. Purchasing a meal-in-a-box kit just doesn't appeal to me. I hate to follow a recipe because it stifles my creativity. I inherited this from my father, who had to add ingredients to a can of pizza sauce, just to make it unique. Recently, I received an e-mail from a major food manufacturer promoting a week of meals made from a single bag of groceries. Skeptical, I tried it and was amazed that I could create the same great meals and still experience the joy of cooking by purchasing grated cheese and pre-cooked chicken. I got the same great homemade results, with semi-homemade ingredients.
The semi-homemade approach of using commercial fired ceramic products can provide you with consistent, high-quality results and save you time as well-time that you can spend on producing your work of art. Scott Causey, a renowned ceramic artist known for his glazing techniques, supports the use of commercial fired products in his work. "As a ceramic artist who had made my own glazes for years, I discovered commercial glazes in my senior year of art school," said Causey. "This was an exciting new medium for me, and I anxiously began trying them all. I made my choices based on test tiles supplied by each glaze company represented in my local craft store. After only a few years, my shelves stood witness to the glaze brand that I knew delivered the best color quality, firing constancy and the widest spectrum of colors to select from."
Commercial underglazes, glazes and overglazes provide consistent results-results that any pottery producer can be proud of.
UnderglazesMany ceramists credit the fun of design work with underglazes for much of the creativity of ceramics. Underglazes have a fascinating number of uses, everything from signing the ware on the bottom of the piece to the finest of brushwork.
As their name implies, underglazes are ceramic colors that are used under a glaze. The two main types of underglazes are translucent and opaque.
Translucent underglazes are used for brushwork and have a definite see-through quality. Normally, one color will show through another applied over it.
Opaque underglazes are used for solid-color coverage over large and small areas. Normally, if one color is applied over another, the base color will not show through.
If necessary, underglazes are thinned with water or a thinning product before application. Most decorating techniques will specify the consistency to which the underglaze colors should be thinned. For normal applications, most underglazes are in a ready-to-use consistency, which is often expressed in terms of everyday dairy products such as thin milk, milk, light cream, cream, and so on. The exception is "wash," which is a watercolorist's term applied to underglazes with a very watery consistency.
GlazesMuch of the beauty and mystery of ceramics comes from the pure magic of glazes. From the shining, glass-like brilliance of a clear gloss glaze to the surprising realism of a color-flecked glaze, the wonderful transformation we see after the glaze firing is one of the primary reasons for the eternal fascination of ceramics.
Because ceramic glazes are available in a variety of colors and surface textures, and since the fired finish is so dramatically different in appearance from the liquid glaze, it is helpful to understand the characteristics of each glaze. Glazes are commonly defined by how much color and transparency they have and fall into one of four categories: opaque, semi-opaque, transparent (colored) and clear.
Opaque glazes are generally used for solid-color coverage on smooth or slightly detailed bisque ware. Generally, underglazes are not used with opaque glazes because only the darkest colors will show through the glaze.
Semi-opaque glazes are best used for solid-color coverage over detailed bisque ware. Some dark underglazes will show under semi-opaque glazes, however, so testing is recommended. If using a semi-opaque glaze on smooth bisque ware, use extra care in application to avoid streaking.
Transparent (colored) glazes are ideal over underglazes to highlight and add an accent of color. Dark glazes might alter the underglaze color, while light-colored glazes will not. Transparent colors are also recommended for single-color application over highly detailed bisque ware, as the color will tend to be intense in the crevices (self-antiquing).
Clear glazes contain no color and produce a clear finish when applied to straight bisque. Underglazes have no color distortion, making clear glazes a wonderful choice to seal and beautify detailed underglaze work.
OverglazesOverglazes are ceramic products designed for application over a fired glaze. The three basic types of overglazes are metallics, lusters and china paints.
Metallics are real precious metals applied to fired glazed ware as the final finish. They are opaque with the brilliance of 22-karat yellow gold or white gold. Their appearance is determined by the glaze on which the metallic is applied. On a gloss glaze, the metallic will be shiny; on a matte glaze, the metallic will be dull. Metallic overglazes are normally applied over a fired glaze but can also be applied to unglazed high-fired porcelain or stoneware bisque.
Lusters are metallic compounds that are applied as a final finish on fired glazed ware and become iridescent after firing. They are translucent with a lustrous iridescence; their appearance is determined by the glaze that the luster is applied over (gloss glaze, shiny luster; matte glaze, dull luster).
China Paints are mineral colors applied in design or as detailing over fired glazed ware.
Success with overglazes depends on correct preparation of the ware to which they will be applied. First, fire the greenware to witness cone 04, then glaze and fire the pieces to witness cone 06. Next, clean the surface of the ware by buffing with soft cloth or by wiping it with a lint-free cloth moistened with isopropyl (rubbing) alcohol to remove hand grease and dirt. (Be sure ware is dry before applying overglazes.) After the ware has been cleaned, avoid excessive handling. When using overglazes, work in a clean, dust-free area with good ventilation. Your hands must be free of all oils, hand lotion and moisture.
Choose any brush with soft hair that will produce the coverage or strokes you wish to achieve. Brushes used to apply overglazes should be cleaned with an overglaze cleaner and wiped on a paper towel. Brushes must be thoroughly dry before use, and each brush should be reserved for exclusive use with only one overglaze to prevent contamination.
Possible Glazing ProblemsEven with commercial glazes, problems can occur if the glazes are used incorrectly or if the ware is not prepared properly. Following are some of the most common glazing problems encountered by artists and potters:
- Using Underfired Bisque. Immature or underfired bisque is the primary cause of flaws and defects in the fired glaze finish. Crazing, pinholes, craters, bare spots and graying of colors are just some of the problems that underfired bisque can create. For best results, apply glazes to bisque that has been fired to witness cone 04. Do not stack ware, overload the kiln or fire on a fast-fire cycle when firing the bisque ware. Always use witness cones on each shelf of the kiln so that you will know the actual temperature reached on each shelf.
- Applying Colors to Dirty Bisque. A dusty bisque surface can cause problems such as bare spots, crawling and pinholes in the fired glaze finish. Because dust can accumulate on bisque stored on open shelves, make it a habit to damp-sponge your bisque before applying a glaze.
- Firing Glazes on Greenware. Firing glazes on greenware is an unsatisfactory shortcut to a finished object and, more often than not, will produce a less-than-perfect finished piece. Gases are released from the clay when firing greenware. If you apply a glaze over greenware, gases will be released through the glaze. This can cause imperfections in the glazed surface. Clay bodies across the country differ from one another, and although a manufacturer can perfect a glaze that will perform beautifully on a greenware clay body that is available in a particular region, there is no way to guarantee that the glaze will perform the same on all clay bodies.
- Firing Greenware and Glazed Bisque Items Together. Moisture, along with the gases, is always found in a greenware kiln firing, and this moisture can contaminate some glaze colors. For this reason, separate firings are always recommended for greenware pieces and glazed bisque pieces.
- Firing Incompatible Glazes Together. When incompatible glazes are fired together, fumes and sputtering from one glaze can cause another glaze to fade in color or acquire black spots. Always check the labels of the glazes you use for any firing instructions. For example, with Duncan Enterprise's product labeling system, all copper-formula glazes, which contain small amounts of copper to enhance color, are labeled as "COPPER FORMULA GLAZE." There are a few other Duncan glazes that, because of their formulation, should not be used or fired with copper-formula glazes, and these glazes are identified on the label by "DO NOT FIRE WITH COPPER-FORMULA GLAZES."
Express YourselfCommercial fired products allow you to focus on your masterpiece without the worry and inconsistency of producing underglazes, glazes and overglazes. Additionally, commercial fired products provide a wide range of color and finish options. With these products, your attention can be dedicated to your masterpiece-an expression of yourself.
SIDEBAR: Glaze Tips
- Start with a good, hard bisque piece fired to at least witness cone 04.
- To remove dust, damp-sponge the bisque for a final cleanup.
- Make sure your work area is clean and that your hands are free of any oil, hand lotion and salt.
- Follow the application techniques recommended on the glaze label.
- Be sure that all the glazes you fire in a kiln load are compatible with each other.
- Keep pieces at least 1/2-in. apart to prevent contamination due to fumes from another glaze.
- Vent the kiln according to the kiln manufacturer's instructions and fire to the recommended cone temperature.
- Avoid a long or extended firing cycle or a short, fast firing. Glazes do best when fired under a normal and consistent temperature range.
- Keep jars tightly closed when not in use.
- If overglaze is accidentally applied, dip a cotton swab in an overglaze cleaner and wipe off the misplaced color.
- If any areas are missed, go back and touch up those areas before either the metallic or luster overglaze dries.
- When planning a project, be sure to check the label of the glaze you want to use. If the label states "overglaze compatible," you can safely use overglazes over the fired glaze.