Sourcing raw materials: a cautionary tale: a diverse and thorough knowledge of raw materials is the potter's only recourse in the present environment of fewer material options.(Pottery Production Practices)

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.

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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 …