Ceramic artists who choose to fire their work in an electric kiln have a broad spectrum of colorants with great predictability available to them. Learn more about those options and how to use them in the guide below.
Defining the Terms
Colorants: Added to a colorless transparent or opaque glaze to create a colored glaze. Colorants can be raw metal oxides or man-made powders smelted from metal oxides and stabilizer mixes into stains. Unlike stains, which are prefired, the color of raw colorant powders often bears no resemblance to the color they produce in a glaze. Raw metal oxide powders are often available as carbonates or oxides. Not all metal oxides produce color (e.g. tin, titanium, zircon), but they can affect existing color, stabilize it, or opacify the glass.
Encapsulated Stains: Made by special processes that coat the individual particles (i.e. cadmium) with silica or zirconium. In this way, they can be suspended in a melt with minimal dissolution of the harmful metals into the glaze.
Glaze Color
Many contemporary ceramic artists seek a variety of colors they can use to add layers of information and/or emotion to a piece of ceramic work. One of the most persuasive reasons for working in the electric kiln is the reliability one can have with a broad spectrum of available colors.
We achieve these colors by accessing minerals that have color as an attribute. Only minerals can survive the heat of the kiln, and since not every colored mineral can survive these temperatures, only a select group of them are useful to the ceramic artist. Some of these minerals come as colored clays, some as minerals found in nature, and some are naturally occurring and are then modified in a lab to suit our needs. We call the minerals found in nature oxide colorants and the minerals that have been modified to suit our needs prepared stains.
Clay as Color
Almost all glaze recipes contain clay. Clay is a source of alumina and silica in glazes. It also serves to make the glaze easier to use by keeping it in suspension. Another very important aspect of clays in a glaze is their contribution to glaze color. Often, we add clays that are white or cream in color. We use these to make colorless transparent glazes and white or cream-colored glazes.
The contribution to glaze color from colored clays is particularly significant to ceramic artists who fire in the electric kiln. Colored clays are especially useful when used as glaze colorants because their rich, warm tones are otherwise difficult to obtain in an electric-kiln firing. They contribute warm ivory, cream, earth orange, red, and brown colors.
In most places, it is easy to find iron-rich clay for use in glazes. In North America, we can use Cedar Heights Redart, a widely distributed red clay. While it is best known as an ingredient in clay bodies, Redart is a fine glaze clay. Glazes that contain Redart are reliable, durable, and visually appealing.
Oxide Colorants
Metallic oxides are important sources of ceramic color. They are minerals found in nature and then mined and refined. Ceramic artists add them to the glazes in varying amounts, usually 1–5% of the total recipe. Their unfired color does not reflect the color they will have when they are fired. This color change introduces unpredictability in the glazing process. When you use colorants, you never know exactly how the piece will look until it is fired. In time you can become familiar with the color changes that take place in the firing and learn to expect them; however, even an experienced ceramic artist will encounter the occasional surprise from a glaze firing.
Be aware that some colorants are toxic. Glazes formulated with toxic metallic oxides can leach these toxic metals if they are used on functional ware surfaces that come in contact with food. Stains can be used as a substitute for some of the toxic colorants, and in other cases, no appropriate colorant or stain may be available.
Commercially Prepared Stains
Stains encourage the broadest color range and include most of the colors available to artists who work in any art media, including the brightest varieties of orange, yellow, burgundy, violet, and pink in ceramics. Initially stains were formulated specifically for low fire, though many stains now can go to the mid-fire temperature range with no problem. There are also encapsulated stains that can survive the high-fire temperature range without any loss of brightness.
Although commercially prepared stains have their source in minerals found in nature, these minerals are modified greatly for the use of ceramic art. They are refined, combined with other coloring minerals, mixed with silica and alumina, fired to bond the various materials, and ground to create a fine powder.
Stains have created a whole new color palette for the ceramic artist. The colors are brilliant, safe to use, and very reliable. One of the most positive characteristics of commercial stains is that their color does not change during the firing. This is because these stains have already been fired during their manufacture. This will enable you to make a reasonable prediction of the way the piece will look after the firing. Stains are added to the glaze in varying amounts, usually 4–15% of the total recipe.
While stains are relatively expensive, they have certain advantages over naturally occurring colorants. Because they are fired in a silica/alumina base and are bonded with that base, they are safe for the maker and user. They are products of industry and, as such, are more predictable and reliable than oxide colorants. Perhaps most importantly, they give the ceramic artist the widest variety of color choices.
Using Stains
Those who use commercially produced glazes are already working with prepared stains. The manufacturers of these glazes use commercially produced stains because of their wide color range and the brilliance of many of the colors. They place great value on the consistency and predictability of their products. The benefits of a wide color range are obvious. Not so obvious are the benefits of consistency and predictability. The manufacturers have found that their customers place a very high value on predictability. If the customers feel that one of these glazes has been modified, they complain.
Stains can also be added to studio-made glazes. The availability of brilliant color is very appealing and many ceramic artists who make glazes from dry ingredients use prepared stains for this purpose.
There are many stain types. Stains can be very sensitive to the glaze ingredients they are added to; their color is heightened or diminished depending on the materials in the recipe. Listed below are the color characteristics of some stain types. Here are a few common types that work well.
Excerpted from Electric Kiln Ceramics: A Guide to Clay, Glazes, and Electric Kilns by Richard Zakin and Frederick Bartolovic. Published by The American Ceramic Society and available at the Ceramic Arts Network Shop, ceramicartsnetwork.org/shop.
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Ceramic artists who choose to fire their work in an electric kiln have a broad spectrum of colorants with great predictability available to them. Learn more about those options and how to use them in the guide below.
Defining the Terms
Colorants: Added to a colorless transparent or opaque glaze to create a colored glaze. Colorants can be raw metal oxides or man-made powders smelted from metal oxides and stabilizer mixes into stains. Unlike stains, which are prefired, the color of raw colorant powders often bears no resemblance to the color they produce in a glaze. Raw metal oxide powders are often available as carbonates or oxides. Not all metal oxides produce color (e.g. tin, titanium, zircon), but they can affect existing color, stabilize it, or opacify the glass.
Encapsulated Stains: Made by special processes that coat the individual particles (i.e. cadmium) with silica or zirconium. In this way, they can be suspended in a melt with minimal dissolution of the harmful metals into the glaze.
Glaze Color
Many contemporary ceramic artists seek a variety of colors they can use to add layers of information and/or emotion to a piece of ceramic work. One of the most persuasive reasons for working in the electric kiln is the reliability one can have with a broad spectrum of available colors.
We achieve these colors by accessing minerals that have color as an attribute. Only minerals can survive the heat of the kiln, and since not every colored mineral can survive these temperatures, only a select group of them are useful to the ceramic artist. Some of these minerals come as colored clays, some as minerals found in nature, and some are naturally occurring and are then modified in a lab to suit our needs. We call the minerals found in nature oxide colorants and the minerals that have been modified to suit our needs prepared stains.
Clay as Color
Almost all glaze recipes contain clay. Clay is a source of alumina and silica in glazes. It also serves to make the glaze easier to use by keeping it in suspension. Another very important aspect of clays in a glaze is their contribution to glaze color. Often, we add clays that are white or cream in color. We use these to make colorless transparent glazes and white or cream-colored glazes.
The contribution to glaze color from colored clays is particularly significant to ceramic artists who fire in the electric kiln. Colored clays are especially useful when used as glaze colorants because their rich, warm tones are otherwise difficult to obtain in an electric-kiln firing. They contribute warm ivory, cream, earth orange, red, and brown colors.
In most places, it is easy to find iron-rich clay for use in glazes. In North America, we can use Cedar Heights Redart, a widely distributed red clay. While it is best known as an ingredient in clay bodies, Redart is a fine glaze clay. Glazes that contain Redart are reliable, durable, and visually appealing.
Oxide Colorants
Metallic oxides are important sources of ceramic color. They are minerals found in nature and then mined and refined. Ceramic artists add them to the glazes in varying amounts, usually 1–5% of the total recipe. Their unfired color does not reflect the color they will have when they are fired. This color change introduces unpredictability in the glazing process. When you use colorants, you never know exactly how the piece will look until it is fired. In time you can become familiar with the color changes that take place in the firing and learn to expect them; however, even an experienced ceramic artist will encounter the occasional surprise from a glaze firing.
Be aware that some colorants are toxic. Glazes formulated with toxic metallic oxides can leach these toxic metals if they are used on functional ware surfaces that come in contact with food. Stains can be used as a substitute for some of the toxic colorants, and in other cases, no appropriate colorant or stain may be available.
Commercially Prepared Stains
Stains encourage the broadest color range and include most of the colors available to artists who work in any art media, including the brightest varieties of orange, yellow, burgundy, violet, and pink in ceramics. Initially stains were formulated specifically for low fire, though many stains now can go to the mid-fire temperature range with no problem. There are also encapsulated stains that can survive the high-fire temperature range without any loss of brightness.
Although commercially prepared stains have their source in minerals found in nature, these minerals are modified greatly for the use of ceramic art. They are refined, combined with other coloring minerals, mixed with silica and alumina, fired to bond the various materials, and ground to create a fine powder.
Stains have created a whole new color palette for the ceramic artist. The colors are brilliant, safe to use, and very reliable. One of the most positive characteristics of commercial stains is that their color does not change during the firing. This is because these stains have already been fired during their manufacture. This will enable you to make a reasonable prediction of the way the piece will look after the firing. Stains are added to the glaze in varying amounts, usually 4–15% of the total recipe.
While stains are relatively expensive, they have certain advantages over naturally occurring colorants. Because they are fired in a silica/alumina base and are bonded with that base, they are safe for the maker and user. They are products of industry and, as such, are more predictable and reliable than oxide colorants. Perhaps most importantly, they give the ceramic artist the widest variety of color choices.
Using Stains
Those who use commercially produced glazes are already working with prepared stains. The manufacturers of these glazes use commercially produced stains because of their wide color range and the brilliance of many of the colors. They place great value on the consistency and predictability of their products. The benefits of a wide color range are obvious. Not so obvious are the benefits of consistency and predictability. The manufacturers have found that their customers place a very high value on predictability. If the customers feel that one of these glazes has been modified, they complain.
Stains can also be added to studio-made glazes. The availability of brilliant color is very appealing and many ceramic artists who make glazes from dry ingredients use prepared stains for this purpose.
There are many stain types. Stains can be very sensitive to the glaze ingredients they are added to; their color is heightened or diminished depending on the materials in the recipe. Listed below are the color characteristics of some stain types. Here are a few common types that work well.
Excerpted from Electric Kiln Ceramics: A Guide to Clay, Glazes, and Electric Kilns by Richard Zakin and Frederick Bartolovic. Published by The American Ceramic Society and available at the Ceramic Arts Network Shop, ceramicartsnetwork.org/shop.
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