The audio file for this article was produced by the Ceramic Arts Network staff and not read by the author.
“Your favorite clay body or glaze material is no longer available.” These are upsetting words no potter ever wants to hear. However, if you’re in ceramics long enough, this fact is a certainty. One’s first thought is why did this happen? Raw material supply and demand play significant parts in the larger industrial market. It is important to know what drives the demise of a raw material. Potters represent less than 1/10% of the raw material market in the US. The vast percentage of other customers dictates the availability and quality of the raw materials used in their industries. We are at the tail end of this economic supply chain and have no choice in dictating whether a raw material stays in production or in its quality.1
Nothing Stays the Same
The only thing constant about ceramics is its inconsistencies. Think of ceramic raw materials as a train. Sometimes the train moves fast, and the supply stops or the material substantially changes. Sometimes the train moves slowly, with a consistent supply, and the materials stay the same. Sometimes the train moves extra slowly, the supply is inconsistent, and the materials subtly alter over time. This is the worst case, as many clay and glaze formulas shift, resulting in a difficult diagnosis of problems. What is important to understand is that the train is always, always moving. In short, from the chemical composition of raw materials to their availability, nothing stays the same.
Understanding the larger raw material market will offer the tools to enact the substitutions that will eventually be required in clay body and glaze formulas. Perversely, all of the discontinued materials are geologically present; it’s just not profitable to sell them to large-scale customers. For example, Albany slip, a low-temperature, high-iron content clay, has been mined since the 1850s and sold throughout the eastern US. However, its volume users no longer need it for the adhesive medium on grinding wheels or glazed areas on ceramic electrical parts, and it was discontinued in 1983. There are still deposits of Albany slip under an asphalt parking lot in the city of Albany, New York.2
With the latest interruption or possible demise of E.P.K. (Edgar’s Plastic Kaolin, a popular secondary kaolin used for its white color, particle size, and plasticity in clay body formulas, contributes alumina and silica to glaze formulas and keeps glazes in suspension), a popular kaolin used in clay body and glaze formulas, potters will once again have to search for a substitute. Currently, Pioneer kaolin has been offered as a suitable substitute. Confusingly, E.P.K., as with other discontinued materials, can still be found in many potters’ studio stockpiles, leading some to believe it can be reordered when their existing supply is exhausted. Additionally, clay body and glaze formulas printed in books, magazine articles, and potters’ notebooks using E.P.K. still require a material that is no longer available.
Materials Can Change Over Time
While large-volume industrial users dictate quality control parameters, the shifting composition of raw materials in particle size, milling conditions, chemical components, organic content, methods of extraction, storage temperature, and humidity levels can all be subject to variations. What can be misleading is that just because the name on the bag stays the same, it does not mean the material inside stays the same.
In the past, NYTAL HR 100 talc was the standard in the ceramics industry and among potters. With its demise, Texas talc came on the market, and then it was discontinued. Presently available is BT 22113 talc mined by IMI Fabi, LLC.
G-200 feldspar is another material changing over time with multiple variations, two of which are G-200 HP (high Potassium) and a blend of G-200 and another feldspar to duplicate the original G-200 feldspar. Currently, it is available as G-200 EU (imported European feldspar).3
Cornwall stone, a feldspathoid which is used in clay body and glaze formulas as a flux, has, over the past few years, gone through several versions, leaving potters questioning which raw color version will work in their glazes.4
Kentucky ball clay OM #4 in the past was mined from a single pit. However, in the mid-1970s, this popular clay was blended with other deposits to ensure uniformity and duration of future supply.
Potters of a certain age will remember using P.B.X., a high-iron content fireclay, Pine Lake fireclay, North American fireclay, Green Ribbon fireclay (a blend of Lincoln fireclay and other clays to approximate Greenstripe), and A.P. Green fireclay (availability can be inconsistent), all of which are no longer in production. In some instances, before a raw material is discontinued, many pounds of it are not processed correctly, have significant chemical changes, or contain gangue (non-plastic materials and contaminants). These events have happened in the past with many fireclays. Potters often do not discover the degradation of materials until they open their kilns.
Fireclays
Fireclays are often the weakest part of a clay-body formula. Some fireclays contain impurities such as lignite (Coal formed with decomposed plant material found in several types of clay. If not completely removed in the firing process, a gas is formed causing bloating.), coal, or high free silica (quartz) content, which the larger users, such as steel and refractory industries, do not consider contaminants because they do not affect their processes or products. However, they are often the cause of clay body bloating (organic material trapped in clay), cooling cracks (quartz inversion), glaze pinholes, and blisters (incomplete volatilization of organic materials exiting the clay as a gas). Depending on the mesh size of the particular fireclay used in clay-body formulas, large nodules of iron result in irregularly shaped brown spots in reduction atmospheres. Blebs (A non-standard technical term first used at Alfred University circa 1972, describing crusty black spit-outs of decomposed manganese nodules. This defect occurs on the clay body surface when fired in a reduction atmosphere.) of manganese can cause spit-outs with concave or convex black defects in reduction atmospheres.
For potters, fireclays contribute “tooth” or stand-up ability in throwing or handbuilding. They reduce fired shrinkage and warping, and allow for strength at high temperatures. However, when they fail in quality, clay-body defects are more prevalent.
Consistent Raw Materials
Since the commercial industrial market controls most, if not all, materials used by potters, they also dictate the quality control parameters of materials used in commercial or industrial applications. A mine or processing plant would not sell to large-volume users if its product was inconsistent. Potters can take advantage of this built-in quality control when ordering these raw materials. However, a material can be discontinued at any point if one or more volume users do not require it in their products. Or a large customer of feldspar X changes its specification for their product. The altered feldspar might not fit the potter’s requirements.
Some of the readily available, quality-controlled materials available to potters are:
Silica: Used in paint, brick, sandpaper, kiln furniture, roof shingles
Feldspars: Used in paint, industrial frits, textile fiberglass, composite reinforcement
Whiting: Used in frit formulation, cement, concrete fillers, plaster, mortars
Dolomite: Used in sanitary ware, steel making flux, soil conditioning, concrete filler
Talc: A filler in plastics, rubber, paper, cosmetics, medicinal pills
Kaolin: A coating in paper, filler in paint, additions to rubber
Ball Clay: Used in cement, sanitary ware, as filler in various applications
Substituting Feldspars
If you mix your own glazes or clay body formulas, at some point, a feldspar substitution will be required. Whether you do not have the feldspar in your studio or it has gone out of production, choosing the right feldspar is essential. Interestingly, you can estimate the age of a potter by which feldspar they recognize from when they first started in ceramics. For example, if a potter references the excellent qualities of Buckingham feldspar, they are in their 60s or 70s. On the opposite end, potters knowledgeable about Mahavir feldspar, a current addition to stock, are much younger.
Feldspars are found in igneous minerals caused by the solidification of magma, which covers a significant percentage of the Earth. Luckily for industry and potters they are mined in large deposits. Feldspars are the major fluxes in glaze and clay-body formulas at cone 9 (2300°F (1260°C)) and cone 6 (2232°F (1222°C)). They melt and facilitate the fusion of other glaze materials, as well as rendering their alkalis of sodium, lithium, and potassium relatively insoluble.
Why is it important to classify feldspars? When it is time to make a substitution, several options exist. One method of classifying feldspars is by their major alkali content: sodium, potassium, or lithium. For example, Minspar 200 contains more sodium than potassium; therefore, it is classified as a sodium feldspar. The same system is used when other feldspars are classified by their predominant alkali levels, whether potassium or lithium are also present. For the purpose of classification, a feldspar’s alumina and silica content are not relevant.
One method to determine whether a feldspar is sodium, potassium, or lithium based is its chemical analysis, which is available from the ceramics supplier. For example:
The higher level of Na2O (0.25) as opposed to K2O (0.10) indicates Gulgong is a sodium-based feldspar. With this in mind, any other sodium-based feldspars can be used as a one-for-one substitute, such as Minspar 200 or, in many instances, Nepheline Syenite. However, it is always best to test any substitution. Nepheline Syenite is not a true feldspar but is classified as a feldspathoid mineral. It supplies potassium, sodium, and alumina, but has less silica than feldspars. For substitution purposes, it can be considered a sodium-based feldspar, but due to its lower silica content, it can cause increased fluxing in some glaze formulas.
The feldspars listed in the table on page 55 might still be found in studio storage bins, may be discontinued, or are still being produced in the US. The classification of foreign feldspars can be arrived at by obtaining their chemical analysis and noting which percentage of potassium or sodium is higher (see feldspar chart).
Raw Material Substitutions
There are several levels of difficulty when considering a glaze material substitution. Even the most closely aligned substitution can cause a different outcome than expected. Many glaze formulas were first developed using a feldspar, clay, or other raw materials, which are no longer in production. Potters can make the mistake of using a raw material in their studio thinking it is still being sold in the ceramics market. For example, Oxford feldspar, a potassium-based alkali alumina silicate, is no longer being mined. If you have a container of Oxford feldspar in your studio and use it in a glaze, there might not be a readily available re-supply.
In some instances, even if the raw material is still in production, it might have subtly changed in chemical composition, particle size, or organic content, all of which can alter the glaze result. Often, ceramics suppliers are unaware of changes in the raw materials they sell. The best course of action, though time consuming and inefficient, is to test raw materials before committing to a production glaze batch.
Another potential source of error occurs when potters use an inappropriate substitute material in the glaze or clay-body formula. For example, when requiring Custer, a potassium-based feldspar, do not use Minspar 200, a sodium-based feldspar. Feldspars used in glaze and clay-body formulas should be substituted within their groups, which are sodium, potassium, and lithium.
Substitute Clays from Within the Same Group
There are several classifications of clays:
Bentonites: One of the smallest-sized platelet clays and extremely plastic. In glaze formulas, 1–2% will keep a liquid glaze in suspension.
Earthenwares: Low-temperature clays, some containing high amounts of iron. In clay-body formulas, they contribute to brown fired colors. In glazes, they introduce iron along with alumina and silica.
Ball Clays: Very plastic clays when used in stoneware clay-body formulas. In glaze formulas, they keep the liquid in suspension while contributing alumina and silica.
Stoneware Clays: Less plastic than ball clays, frequently used in high-temperature stoneware clay-body formulas. They contribute to platelet size variation in clay-body formulas. Less frequently or not at all used in glaze formulas.
Kaolins: High-temperature, white clays used in porcelain or white stoneware clay-body formulas. Kaolins are used in glaze formulas for their alumina and silica content.
Fireclays: High-temperature clay, not as plastic as ball clays, kaolins, or stoneware clays. Not used in glaze formulas. Fireclays are the most inconsistent in quality control. They can contain carbonaceous materials such as lignite, peat, coal, and tramp materials. Fireclays can also have variable particle sizes of silica, iron, and manganese; the last two metallic oxides can deform and disrupt the surfaces of fired glazes as brown or black blemishes.
Substituting Metallic Coloring Carbonates
At some point, we have all run out of a metallic coloring oxide when mixing a glaze formula. The general rule is: 1½ times more carbonate will equal one part of the oxide. For example, if a formula calls for 1 part cobalt oxide, we can use 1½ parts of cobalt carbonate, which should yield approximately the same color intensity. While this is not the exact ratio (1.59 is the exact ratio), it will produce functionally correct color intensity.5 In satin or matte glazes, cobalt oxide can yield a blue field of color with blue specking due to its larger particle size when compared with the smaller particle size of cobalt carbonate. The same ratios in reverse can be used for substituting metal coloring oxides for their carbonate forms.
Difficult Replacements
Because of their unique chemistry, some clays are difficult to substitute on a one-for-one basis. Most notable are Albany slip and Barnard clays. While some suppliers have tried to put forth substitutes, at best, some work in limited situations. Newman Red, a high-iron content, low-range stoneware clay, is another clay with unique qualities that has gone out of production. On a broader scale, there are numerous local small-deposit clays that have a limited market or high mining cost.
Commercially Prepaid Moist Clay
A discontinued material affects not only potters but also the companies that mix clay for the wider ceramics market. For ceramics suppliers, there is an economic cost in finding and then substituting a material.
A difficult problem for suppliers is whether to notify customers of the change in material. If the actual clay-body performance stays the same, is a notification warranted? Consistently reliable moist clay is critical in securing a potter’s trust.
A Ceramics Education
Since the availability of any given raw material is an unknown, one tool a potter can acquire and sharpen is knowledge of the chemistry and physical properties of materials used in clay-body and glaze formulas. While this seems at first to be an overwhelming subject, one piece of information might get you started: Over 80% of glaze formulas contain just 1 to 12 raw materials in different amounts and ratios, and that narrows the field of study down considerably.
Acknowledgments: Jim Fineman, my technical editor and a professional potter.
the author Jeff Zamek started his career 48 years ago. He obtained BFA/MFA degrees in ceramics from Alfred University, College of Ceramics, New York. In 1980, he started Ceramics Consulting Services, a ceramics-consulting firm developing clay body and glaze formulas for ceramics supply companies throughout the US. His books, The Potter’s Studio Clay & Glaze Handbook, What Every Potter Should Know, Safety in the Ceramics Studio, and The Potter’s Health & Safety Questionnaire are available from Jeff Zamek/Ceramics Consulting Services. For technical information, visit www.jeffzamek.com.
1 “The Economics of Pottery Production,” Pottery Production Practices, February 28, 2005. 2 “No More Albany Sip, No More Barnard/Blackbird,” Studio Potter, June 2006. 3 “The History of G-200 Feldspar,” Ceramics Technical, No 38, 2014. 4 “Old and New Cornwall Stone,” Ceramics Technical, No. 33, 2011. 5 Other metallic carbonate to oxide ratios are: 1.4 parts copper carbonate equals 1 part copper oxide, 1.7 parts manganese carbonate equals 1 part manganese dioxide.
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The audio file for this article was produced by the Ceramic Arts Network staff and not read by the author.
“Your favorite clay body or glaze material is no longer available.” These are upsetting words no potter ever wants to hear. However, if you’re in ceramics long enough, this fact is a certainty. One’s first thought is why did this happen? Raw material supply and demand play significant parts in the larger industrial market. It is important to know what drives the demise of a raw material. Potters represent less than 1/10% of the raw material market in the US. The vast percentage of other customers dictates the availability and quality of the raw materials used in their industries. We are at the tail end of this economic supply chain and have no choice in dictating whether a raw material stays in production or in its quality.1
Nothing Stays the Same
The only thing constant about ceramics is its inconsistencies. Think of ceramic raw materials as a train. Sometimes the train moves fast, and the supply stops or the material substantially changes. Sometimes the train moves slowly, with a consistent supply, and the materials stay the same. Sometimes the train moves extra slowly, the supply is inconsistent, and the materials subtly alter over time. This is the worst case, as many clay and glaze formulas shift, resulting in a difficult diagnosis of problems. What is important to understand is that the train is always, always moving. In short, from the chemical composition of raw materials to their availability, nothing stays the same.
Understanding the larger raw material market will offer the tools to enact the substitutions that will eventually be required in clay body and glaze formulas. Perversely, all of the discontinued materials are geologically present; it’s just not profitable to sell them to large-scale customers. For example, Albany slip, a low-temperature, high-iron content clay, has been mined since the 1850s and sold throughout the eastern US. However, its volume users no longer need it for the adhesive medium on grinding wheels or glazed areas on ceramic electrical parts, and it was discontinued in 1983. There are still deposits of Albany slip under an asphalt parking lot in the city of Albany, New York.2
With the latest interruption or possible demise of E.P.K. (Edgar’s Plastic Kaolin, a popular secondary kaolin used for its white color, particle size, and plasticity in clay body formulas, contributes alumina and silica to glaze formulas and keeps glazes in suspension), a popular kaolin used in clay body and glaze formulas, potters will once again have to search for a substitute. Currently, Pioneer kaolin has been offered as a suitable substitute. Confusingly, E.P.K., as with other discontinued materials, can still be found in many potters’ studio stockpiles, leading some to believe it can be reordered when their existing supply is exhausted. Additionally, clay body and glaze formulas printed in books, magazine articles, and potters’ notebooks using E.P.K. still require a material that is no longer available.
Materials Can Change Over Time
While large-volume industrial users dictate quality control parameters, the shifting composition of raw materials in particle size, milling conditions, chemical components, organic content, methods of extraction, storage temperature, and humidity levels can all be subject to variations. What can be misleading is that just because the name on the bag stays the same, it does not mean the material inside stays the same.
In the past, NYTAL HR 100 talc was the standard in the ceramics industry and among potters. With its demise, Texas talc came on the market, and then it was discontinued. Presently available is BT 22113 talc mined by IMI Fabi, LLC.
G-200 feldspar is another material changing over time with multiple variations, two of which are G-200 HP (high Potassium) and a blend of G-200 and another feldspar to duplicate the original G-200 feldspar. Currently, it is available as G-200 EU (imported European feldspar).3
Cornwall stone, a feldspathoid which is used in clay body and glaze formulas as a flux, has, over the past few years, gone through several versions, leaving potters questioning which raw color version will work in their glazes.4
Kentucky ball clay OM #4 in the past was mined from a single pit. However, in the mid-1970s, this popular clay was blended with other deposits to ensure uniformity and duration of future supply.
Potters of a certain age will remember using P.B.X., a high-iron content fireclay, Pine Lake fireclay, North American fireclay, Green Ribbon fireclay (a blend of Lincoln fireclay and other clays to approximate Greenstripe), and A.P. Green fireclay (availability can be inconsistent), all of which are no longer in production. In some instances, before a raw material is discontinued, many pounds of it are not processed correctly, have significant chemical changes, or contain gangue (non-plastic materials and contaminants). These events have happened in the past with many fireclays. Potters often do not discover the degradation of materials until they open their kilns.
Fireclays
Fireclays are often the weakest part of a clay-body formula. Some fireclays contain impurities such as lignite (Coal formed with decomposed plant material found in several types of clay. If not completely removed in the firing process, a gas is formed causing bloating.), coal, or high free silica (quartz) content, which the larger users, such as steel and refractory industries, do not consider contaminants because they do not affect their processes or products. However, they are often the cause of clay body bloating (organic material trapped in clay), cooling cracks (quartz inversion), glaze pinholes, and blisters (incomplete volatilization of organic materials exiting the clay as a gas). Depending on the mesh size of the particular fireclay used in clay-body formulas, large nodules of iron result in irregularly shaped brown spots in reduction atmospheres. Blebs (A non-standard technical term first used at Alfred University circa 1972, describing crusty black spit-outs of decomposed manganese nodules. This defect occurs on the clay body surface when fired in a reduction atmosphere.) of manganese can cause spit-outs with concave or convex black defects in reduction atmospheres.
For potters, fireclays contribute “tooth” or stand-up ability in throwing or handbuilding. They reduce fired shrinkage and warping, and allow for strength at high temperatures. However, when they fail in quality, clay-body defects are more prevalent.
Consistent Raw Materials
Since the commercial industrial market controls most, if not all, materials used by potters, they also dictate the quality control parameters of materials used in commercial or industrial applications. A mine or processing plant would not sell to large-volume users if its product was inconsistent. Potters can take advantage of this built-in quality control when ordering these raw materials. However, a material can be discontinued at any point if one or more volume users do not require it in their products. Or a large customer of feldspar X changes its specification for their product. The altered feldspar might not fit the potter’s requirements.
Some of the readily available, quality-controlled materials available to potters are:
Substituting Feldspars
If you mix your own glazes or clay body formulas, at some point, a feldspar substitution will be required. Whether you do not have the feldspar in your studio or it has gone out of production, choosing the right feldspar is essential. Interestingly, you can estimate the age of a potter by which feldspar they recognize from when they first started in ceramics. For example, if a potter references the excellent qualities of Buckingham feldspar, they are in their 60s or 70s. On the opposite end, potters knowledgeable about Mahavir feldspar, a current addition to stock, are much younger.
Feldspars are found in igneous minerals caused by the solidification of magma, which covers a significant percentage of the Earth. Luckily for industry and potters they are mined in large deposits. Feldspars are the major fluxes in glaze and clay-body formulas at cone 9 (2300°F (1260°C)) and cone 6 (2232°F (1222°C)). They melt and facilitate the fusion of other glaze materials, as well as rendering their alkalis of sodium, lithium, and potassium relatively insoluble.
Why is it important to classify feldspars? When it is time to make a substitution, several options exist. One method of classifying feldspars is by their major alkali content: sodium, potassium, or lithium. For example, Minspar 200 contains more sodium than potassium; therefore, it is classified as a sodium feldspar. The same system is used when other feldspars are classified by their predominant alkali levels, whether potassium or lithium are also present. For the purpose of classification, a feldspar’s alumina and silica content are not relevant.
One method to determine whether a feldspar is sodium, potassium, or lithium based is its chemical analysis, which is available from the ceramics supplier. For example:
The higher level of Na2O (0.25) as opposed to K2O (0.10) indicates Gulgong is a sodium-based feldspar. With this in mind, any other sodium-based feldspars can be used as a one-for-one substitute, such as Minspar 200 or, in many instances, Nepheline Syenite. However, it is always best to test any substitution. Nepheline Syenite is not a true feldspar but is classified as a feldspathoid mineral. It supplies potassium, sodium, and alumina, but has less silica than feldspars. For substitution purposes, it can be considered a sodium-based feldspar, but due to its lower silica content, it can cause increased fluxing in some glaze formulas.
The feldspars listed in the table on page 55 might still be found in studio storage bins, may be discontinued, or are still being produced in the US. The classification of foreign feldspars can be arrived at by obtaining their chemical analysis and noting which percentage of potassium or sodium is higher (see feldspar chart).
Raw Material Substitutions
There are several levels of difficulty when considering a glaze material substitution. Even the most closely aligned substitution can cause a different outcome than expected. Many glaze formulas were first developed using a feldspar, clay, or other raw materials, which are no longer in production. Potters can make the mistake of using a raw material in their studio thinking it is still being sold in the ceramics market. For example, Oxford feldspar, a potassium-based alkali alumina silicate, is no longer being mined. If you have a container of Oxford feldspar in your studio and use it in a glaze, there might not be a readily available re-supply.
In some instances, even if the raw material is still in production, it might have subtly changed in chemical composition, particle size, or organic content, all of which can alter the glaze result. Often, ceramics suppliers are unaware of changes in the raw materials they sell. The best course of action, though time consuming and inefficient, is to test raw materials before committing to a production glaze batch.
Another potential source of error occurs when potters use an inappropriate substitute material in the glaze or clay-body formula. For example, when requiring Custer, a potassium-based feldspar, do not use Minspar 200, a sodium-based feldspar. Feldspars used in glaze and clay-body formulas should be substituted within their groups, which are sodium, potassium, and lithium.
Substitute Clays from Within the Same Group
There are several classifications of clays:
Substituting Metallic Coloring Carbonates
At some point, we have all run out of a metallic coloring oxide when mixing a glaze formula. The general rule is: 1½ times more carbonate will equal one part of the oxide. For example, if a formula calls for 1 part cobalt oxide, we can use 1½ parts of cobalt carbonate, which should yield approximately the same color intensity. While this is not the exact ratio (1.59 is the exact ratio), it will produce functionally correct color intensity.5 In satin or matte glazes, cobalt oxide can yield a blue field of color with blue specking due to its larger particle size when compared with the smaller particle size of cobalt carbonate. The same ratios in reverse can be used for substituting metal coloring oxides for their carbonate forms.
Difficult Replacements
Because of their unique chemistry, some clays are difficult to substitute on a one-for-one basis. Most notable are Albany slip and Barnard clays. While some suppliers have tried to put forth substitutes, at best, some work in limited situations. Newman Red, a high-iron content, low-range stoneware clay, is another clay with unique qualities that has gone out of production. On a broader scale, there are numerous local small-deposit clays that have a limited market or high mining cost.
Commercially Prepaid Moist Clay
A discontinued material affects not only potters but also the companies that mix clay for the wider ceramics market. For ceramics suppliers, there is an economic cost in finding and then substituting a material.
A difficult problem for suppliers is whether to notify customers of the change in material. If the actual clay-body performance stays the same, is a notification warranted? Consistently reliable moist clay is critical in securing a potter’s trust.
A Ceramics Education
Since the availability of any given raw material is an unknown, one tool a potter can acquire and sharpen is knowledge of the chemistry and physical properties of materials used in clay-body and glaze formulas. While this seems at first to be an overwhelming subject, one piece of information might get you started: Over 80% of glaze formulas contain just 1 to 12 raw materials in different amounts and ratios, and that narrows the field of study down considerably.
Acknowledgments: Jim Fineman, my technical editor and a professional potter.
the author Jeff Zamek started his career 48 years ago. He obtained BFA/MFA degrees in ceramics from Alfred University, College of Ceramics, New York. In 1980, he started Ceramics Consulting Services, a ceramics-consulting firm developing clay body and glaze formulas for ceramics supply companies throughout the US. His books, The Potter’s Studio Clay & Glaze Handbook, What Every Potter Should Know, Safety in the Ceramics Studio, and The Potter’s Health & Safety Questionnaire are available from Jeff Zamek/Ceramics Consulting Services. For technical information, visit www.jeffzamek.com.
1 “The Economics of Pottery Production,” Pottery Production Practices, February 28, 2005.
2 “No More Albany Sip, No More Barnard/Blackbird,” Studio Potter, June 2006.
3 “The History of G-200 Feldspar,” Ceramics Technical, No 38, 2014.
4 “Old and New Cornwall Stone,” Ceramics Technical, No. 33, 2011.
5 Other metallic carbonate to oxide ratios are: 1.4 parts copper carbonate equals 1 part copper oxide, 1.7 parts manganese carbonate equals 1 part manganese dioxide.
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