Ceramic Industry

POTTERY PRODUCTION PRACTICES: Sourcing Raw Materials: A Cautionary Tale

March 1, 2007
A diverse and thorough knowledge of raw materials is the potter's only recourse in the present environment of fewer material options.   

Albany slip open pit mine.


Once widely used as a glaze material, Albany slip clay is no longer commercially available, and any stockpiles held by potters will eventually be exhausted. This event is predictable when you consider the history of raw materials in the pottery industry. At some point while working in ceramics, one or more of the essential raw materials used in your clay bodies or glazes will become unobtainable.

To add to the confusion, several materials are still listed in glaze and clay body formulas even though they are not being mined. Once they are depleted from potters' storage bins, these materials will not be available from ceramic suppliers or commercial distributors. With this in mind, it is always a good practice to research the availability of any raw material before using it in a glaze formula. When a raw material is no longer available, potters have to develop a suitable substitution that will offer the same effect in glazes and clay body formulas.

In most instances, a material's departure from the market is based on economic justifications and not the actual depletion of the ore, feldspar or clay. For instance, geologic deposits of Albany slip clay still exist, though it is no longer being mined.

History of Albany Slip Clay

Albany slip clay is an alluvial deposit formed by the transportation of material through glacial action in the Albany Hudson River region of New York state.1 It is less refractory and darker than residual clays like kaolins, which are formed on site and are highly refractory and white. Albany slip clay has an intricate mineralogy with high levels of alkalis and irons. It is a hydrous alumino-silicate clay, dark brown and non-plastic, and has a silty texture.2 It is often described as a loose sedimentary material with rock particles of generally 1/20 mm or less in diameter. Potters used this clay for over 250 years.

The northern Hudson Valley of New York State was an active pottery-making region; by the 1840s, almost 60 potters produced and sold ware in and around the city of Albany. The newspaper and sales records of Albany slip clay, commonly called "Albany mud," date back to the Revolutionary War period.3 The newspapers of the 1800s advertised Albany slip clay as a substitute glaze for the toxic lead glazes that were commonly used on functional pottery of the period.

The most distinctive feature of the ware is characterized by an "orange peel" texture on exposed non-glazed fired clay surfaces. The onset of prohibition in the U.S. led to the demise of stoneware crocks and salt-glazed jugs, and coincided with the popularity of mass-produced glass containers. Today a trip to any antiques store will reveal many crocks, jugs and other functional pottery containers that were glazed with Albany slip in the salt firing process, as well as other Albany slip glazed pots.

Numerous glaze variations were formulated using Albany slip clay (a slip clay is a naturally occurring clay that forms a glaze) as the minor or major ingredient. It has also been used as a decorative slip (engobe) applied over a raw glaze on functional ware. At higher temperature ranges above cone 9 (2300°F), Albany slip clay is almost a glaze by itself and is characterized by a glossy flowing surface ranging in color from light yellow/green to dark brown/black in reduction kiln atmospheres.

Due to its high iron content, Albany slip was used in "Temmoku" iron crystal glazes, producing a wide range of glaze effects such as "hare's fur" (light streaks in the glaze) and "tea dust" (small crystals formed in the glaze upon cooling).4 Albany's long history of easily available supply and extensive distribution resulted in its use as a glaze material by many generations of potters. However, due to its lack of plasticity, it was not used extensively in clay body formulas for wheel throwing or hand building.

Albany slip clay had a history of use in commercial pottery production and industry. Rowe Pottery Works, maker of museum- quality reproductions, and Pfaltzgraff Pottery used the clay extensively. Rival Pottery, manufacturer of the Crock-Pot®, used Albany slip as a glaze on its ware as well. Albany slip has been also employed on such diverse applications as electrical insulators, vitreous coatings for structural clay products, and stoneware pottery. This versatile clay was used as a smooth, non-absorbent glazed coating for sewer pipe, and has been employed as a bonding agent on abrasive wheels for over 90 years.

In 1962, Industrial Mineral Products acquired the Albany slip mine, formerly owned by Rex Clay Co., which was located at Prospect Ave. and Livingston Ave. in Albany, N.Y. Hammill & Gillespie, Inc., an importer and distributor of ceramic raw materials, was appointed exclusive agent for distribution of the clay. Hammill & Gillespie continued to supply ceramic supply companies, individual potters and commercial/industrial users with the clay.

The open strip mine a few blocks from the capitol in Albany encountered mounting economic problems, including higher insurance rates, increasing processing costs, fuel costs for trucking, and stricter U.S. Environmental Protection Agency (EPA) regulations. After the extraction of clay, the pit had to be completely covered until the next harvesting. Once the raw clay was removed from the site, it went to the processing plant for grinding, screening, bagging and palletizing. It was then ready for shipping to Hammill & Gillespie's warehouse.

The raw clay had a moisture content ranging between 18 and 23%, which meant that for every 1000 lbs of raw clay extracted from the mine and shipped to the processing plant, 180-230 lbs. was lost, though it still incurred transportation and milling costs. Translating these percentages into actual costs offers a more precise explanation of the financial requirements to bring Albany slip clay to market. A $50,000-$75,000 capital outlay was required to cover mining, transportation, processing, bagging and storage costs to produce an 18-month stockpile.

During this period, the predominant percentage of clay sales was to potters purchasing a few pounds or one or two 50-lb bags, which meant a slow payback on a low-profit material for a large capital investment. The same financial process was required every time a stockpile was exhausted. Such a financial structure for any raw material supplier was vulnerable to a price increase at any point in the processing or distribution process.

The last stockpile of Hammill & Gillespie's Albany slip clay was depleted in 1987. Keep in mind that, as with other discontinued raw materials, Albany slip clay remains in some potters' existing inventories but at present is not to be found in any ceramic suppliers' inventories.

Material Properties

Albany slip clay changed over the years since it was first mined. The three sample analyses shown in Table 1 are "run of the mine," which means the properties can shift from batch to batch. A definitive analysis of any one shipment is often not possible.

The clay was shipped in 50-lb brown bags with black side lettering, and some bags were not marked with production lot numbers. The subsequent variations in chemical analyses of the slip and the variation in potters' kiln firing atmospheres, clay bodies and glaze application methods can account for the variations in the fired glaze. Remember, just because the name on the bag stays the same, what's inside may not be.

Albany slip glazed jug, 1900s Albany slip top, clear glaze bottom (2300°F, approximate height 11 in.).

Finding Substitutions

Due to its unique natural mineral content, which has changed at various intervals during its availability, Albany slip clay has proven somewhat difficult to reproduce either through other slip clays or by building a substitute from duplicating its oxide content. As with other naturally occurring ores like Gerstley borate and Barnard slip clay, there are no definitive chemical analyses of the materials to use as a baseline when considering a substitution. Additionally, trace materials found in the deposit can contribute to unique firing qualities that often do not lend themselves to duplication. In the past, Michigan slip clay was an acceptable substitute for Albany, but it was discontinued in the 1970s.

When a raw material is no longer available and potters exhaust their own supply, there is always a rush to find adequate substitutes. Unfortunately, many raw materials are unique in chemical composition, trace elements, particle size distribution, handling characteristics and organic content, and do not lend themselves to a one-to-one substitution suitable for every temperature range and kiln atmosphere. In the past, ceramic supply companies rushed to sell substitutes, which sometimes did not yield the desired results. Potters have often stockpiled reserves of the original raw material, which can tie up money and studio storage space.

Several Albany slip substitutes work quite well in various glaze formulas; however, none of the substitutes will work in every glaze formula exactly like the original Albany slip clay. Therefore, as is the case when using any substitute material, it is advisable to test it in a small batch of glaze and see the results in your own production kiln, not a small test kiln. Price should never be a consideration when choosing a substitute, since the cost of any raw material is insignificant when compared to the time and labor used to create and fire the ceramic ware. In any situation, if a substitute material works, pay the price.

Orphan Ores

When large industries abandon the use of a raw material, the limited pottery market does not have the buying power to sustain its production. Orphan ores are ceramic raw materials that are left without viable market support. Small raw material buying markets, such as potters and ceramics suppliers, do not order sufficient volume to sustain raw material production.

Moreover, there is a delicate balance between the cost of mining, processing and shipping the material compared to the price potters are willing to pay for the material. If any cost of production increases while bringing a raw material to market, it becomes unfeasible to substantially increase the price to the eventual user.

One or more of the following characteristics describe materials that have a high probability of becoming unavailable to potters:
  • There was once a viable economic basis for their production.
  • They currently do not have large and diverse industrial or commercial markets.
  • They have increasing processing costs vs. low selling prices.
  • They are used in products that have low intrinsic resale value (i.e., pottery).
  • After being dropped from the larger markets, they are still used by limited individualistic markets that purchase small quantities intermittently.


Gold and Raw Materials

What does gold have in common with the raw materials used by potters? Nothing, except as a model of opposite values and their relationship to the marketplace. Gold is relatively scarce and has a very high value and wide market appeal. The current price of gold is $500/oz or $8000/lb. Compare that figure to the last quoted price of Albany slip clay by Hammill & Gillespie, which was $.35/lb. There is an obvious difference between a rare, high-value ore and a common ore of low value with limited market appeal.

What does this mean in terms of supply and demand? The rarity of gold and its intrinsic value means a great many individuals and industries are willing to pay a premium price. Furthermore, there is a high markup on gold jewelry that far exceeds the actual price of the gold itself. The costs of locating, mining, processing and distributing gold are worth the effort based on the perceived value, high retail selling price, and large and diverse market demand.

Albany slip, on the other hand, has a low value with limited market demand. In addition, the endpoint users of the clay-whether individual potters, commercial potteries or industry-are using it in products with small profit margins. The profit margins for mining, processing and distribution of clays and other ceramic raw materials are much lower than that of gold, and are subject to any number of increasing processing and transportation costs as well. The rising cost of transporting the clay often exceeds the actual cost of the material, forcing ceramic suppliers to use clays and raw materials from their immediate geographical area whenever possible.

The lands containing deposits of Albany slip clay are still undeveloped and covered by overgrowth. The site near Prospect Ave. and Livingston Ave. in Albany has been used as a landfill and contains the remains of the Empire Plaza site in Albany. The other mine site, across from North Lake Ave. near the Tivoli Lakes Wildlife Park (also in Albany), is overgrown with weeds. The vacant mine sites illustrate that the land is not presently being used for more profitable commercial enterprises, and that the demise of Albany slip clay was brought about by the increasing production costs associated with bringing the clay to market.

Contemporary salt glazed Albany slip glazed jug (2300°F, reduction fired to cone 9, height 13 in.).

Ceramic Raw Material Economics

A closer examination of why Albany slip clay is no longer available reveals the economic factors that control the entire spectrum of raw materials available to the pottery market. Many of our favorite raw materials are on a precarious balance of profitability to the companies that mine and supply them. Specifically, Albany slip was on an economic knife-edge of profitability during its production life. As we have examined, small changes in mining, processing and shipping resulted in its demise.

Overall, potters represent less than 1/10% of the entire raw material market in the U.S., which translates into little or no buying power in comparison to the larger commercial and industrial users that dictate the supply and quality control parameters of any given material. Individual potters or ceramic suppliers do not purchase in the quantities that guarantee any material will remain consistent in chemical makeup, particle size distribution or future supply. The inequitable buying position potters find themselves in is not brought on by their need for a specific raw material, but by the simple fact that they can't buy enough of that material to guarantee future supplies.

A stable market means that the cost of producing a raw material is often below what potters will pay for it, leaving comfortable profit margins for the miner, processor, wholesale distributor and retail seller. If a raw material has a long chain of intermediate suppliers each making a small profit, any increase in production costs can upset the system and make it uneconomical for supply to potters. Potters purchasing raw materials are largely unaware of mining and processing costs, as well as small distributor profit margins, but they are very aware of the price they will pay for a raw material.

Potters are caught between the unique qualities of making handmade functional objects and their inability to achieve economies of scale through mass production or economies of technology through less costly machine-made ware. In practice, potters have discovered the market for handmade ceramic objects is very small, and the sub-group within that population that will pay $50 for a coffee mug is even smaller. If potters could consistently sell coffee mugs for $50 each, they could then afford to pay a higher price for their raw materials, thus keeping orphan ores in production, or at least giving a greater economic incentive for suppliers to find a substitute.

What can potters do to counter market forces beyond their control? Several strategies can be effective in avoiding a situation where your favorite raw material is no longer available. The first and most useful tool is to learn how raw materials function within clay body and glaze formulas. Potters often know they need a certain feldspar in a glaze formula but do not understand its function or know which other feldspars can be substituted. While there are many substitute materials that will produce the same glaze or clay body color, surface texture, or handling characteristics as the original material, many clay body and glaze formulas can be duplicated by the use of totally different formulas.

Awareness of the current raw material market is essential. While every one of the hundreds of materials do not have to be monitored, it is advisable to keep in touch with your ceramics supplier about the raw materials used in your glaze and clay body formulas. Do not assume that the material is still being produced just because the bin in your studio is full.

Another option, which ties up capital and studio space, is the stockpiling of raw materials in the eventual case one or more might be discontinued. However, this strategy often reflects a static view of ceramics and a potter's inability to manipulate raw materials to achieve functional and aesthetic goals. The economic forces behind Albany slip's demise are still in place, and they will remove more of our favorite raw materials in the future.

The Future of Domestic Raw Materials

Ceramic raw material markets in the U.S. have changed more in the last five years than in the preceding 25. Greater numbers of ceramic products are now being produced in China, Spain, Vietnam, Mexico and other foreign countries that rely on cheaper labor and their own domestic sources of clays and raw materials. Mines and raw material processors in the U.S. are beginning to limit their production due to the domestic lack of demand.

Does this mean all domestic ball clays will be discontinued? No, but a mine might produce 12 vs. 20 different ball clays. At some point, a reduced inventory of clays and other raw materials will again cause potters to look for substitutes for their clay and glaze formulas. A diverse and thorough knowledge of raw materials is the potter's only recourse in the present environment of fewer material options.

Author's Acknowledgements

I would like to thank Dorna Isaacs for her help in supplying technical information and the history of Albany slip clay. I have relied in part on the articles and notes of Richard P. Isaacs, past president of Hammill & Gillespie. Richard L. Lehman, Ph.D., technical director of Hammill & Gillespie, Inc., supplied information on Albany slip clay. Barbara and Dennis Reeley of River Street Pottery (621 River St., Troy, NY 12180) contributed photographs of the Albany slip clay site in 2005 as well as information on the location of Albany slip clay. Photos of the Albany slip mine are from the Hammill & Gillespie archives. Photographs of pottery are from the author's collection.

SIDEBAR: Finding Albany Slip Clay and Substitutes

A 10-ton stockpile of original raw Albany slip clay is available and can be purchased in small or large quantities from The Great American Wheel Works, N.Y. The clay comes with an instruction sheet on how to screen the small pebbles that constitute approximately 1% of the total clay content. Call (518) 756-2368 or e-mail tflitto@msn.com for additional details. Albany slip clay substitutes include:
  • Alberta Slip Clay, a Canadian blended substitute distributed by Laguna Clay Co., 14400 Lomitas Ave., City of Industry, CA 91746 or (626) 330-0631; and Axner Pottery Supply: 490 Kane Ct., P.O. Box 621484, Oviedo, FL 32765 or (407) 365-2600.
  • Arroyo Slip Clay, a naturally occurring slip glaze mineral distributed by Laguna Clay Co.
  • Albany Slip Substitute, Alberta Slip, Ravenscrag Slip (Alberta Slip II), distributed by Bailey Ceramic Supply, P.O. Box 1577, 62 Ten Broeck Ave., Kingston, NY 12402 or (845) 339-3721.
  • Albany Slip Substitute, a blend of Sheffield clay, which is a high-iron-content earthenware clay, and frits,  Sheffield Pottery, U.S. Route 7, P.O. Box 399, Sheffield, MA 01257 or (413) 229-7700.
  • Seattle Slip, a naturally occurring slip clay distributed by Seattle Pottery Supply, 35 South Hanford, Seattle, WA 98134 or (206) 587-0570.