Slipups: Mocha ware at the Shelburne Museum

Mocha ware, with its brightly patterned surfaces and surprisingly modern decoration, has attracted the attention of collectors for many years. (1) Recently, research on the origins of its kaleidoscopic designs has resulted in the publication of important books and articles by Sumpter Priddy, Donald Carpentier, and Jonathan Rickard. (2) In addition, the Shelburne Museum in Shelburne, Vermont, has recently reinstalled its 230 pieces of mocha ware, the largest public collection in the world. The two-year project enabled the museum staff to closely evaluate our holdings, actively acquire important pieces, and most important compare, contrast, and come to our own conclusions regarding the execution of the remarkable surfaces of mocha ware. This article summarizes some of our observations and discoveries. (3)

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A product of the industrial revolution, English mocha ware was mass produced for commercial use in taverns as well as for domestic consumption by the working classes in British, American, and continental markets from the late eighteenth century until the early twentieth century. Although the technology used to manufacture mocha ware was state-of-the-art at the time, the equipment used to produce it lacked the precision and uniformity commonly associated with the automated assembly lines of today. Moreover, the limitations of the available technologies required a high level of handwork on the part of decorators, which, in turn, increased the potential for irregularities. In short, the strikingly colored slip surfaces of mocha ware often reveal the presence of the human hand within the industrial process. Practically invisible or blatantly obvious, these so-called slipups made centuries ago survive today beneath vitrified coats of clear overglaze and provide snapshots of the innovative and ingenious decorative techniques employed. By studying the fanciful surfaces on a select group of mocha ware objects in the Shelburne Museum's collection, we have obtained invaluable clues for deciphering the methods used in their production.

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Inexpensive and easily made, slip--a mixture of clay and water--is a free-flowing and versatile decorating medium that has been used to ornament the porous surfaces of ceramic vessels for millennia. Slip is also fast drying and highly absorbent, making it efficient but unforgiving of human error. Once made, accidents are virtually indelible and can only be corrected by complete removal of the affected surface. In spite of the disadvantages of slip, British manufacturers successfully exploited its versatility and adroitly adapted its ephemeral fluidity to the high volume industrial production of mocha ware. However, both the integrity of the materials and the training of the workforce were crucial to successful mocha ware decoration. If the quality of either was compromised, the resulting decoration suffered.

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As they were competing for the same American, European, and domestic markets, eighteenth and early nineteenth-century Staffordshire potteries emphasized quantity. The economic livelihood of mocha ware decorators depended on their output measured by the tally of their daily production of "good from oven" objects--those that survived the kiln firing in pristine condition. (4) In this fast-paced industrial setting, the decorators focused on stocking the kilns with as many pieces of their work as possible, which ultimately often compromised the finished product. Imperfect surfaces made their way into the market because they were sold at discounted prices as second- or third-grade quality objects.

As demand for ceramic goods increased during the eighteenth and first half of the nineteenth centuries, English potteries--always hotbeds of experimentation--developed and adopted new methods, equipment, and materials to improve their production. Two important innovations for slip decoration were the rose-and-crown engine-turning lathe and the three-chambered slip cup.

During the late 1760s, Josiah Wedgwood (1730-1795) introduced the so-called rose-and-crown engine-turning lathe to the pottery industry. Originally used to produce scored decoration on metalwork, this engine-turning lathe was similar in principle to its counterpart for wood, except that its rotational movement was governed by two types of cams. When used in conjunction with custom-made stationary blades, the peaks and valleys of the sprocket-shaped edge cam (or rose cam) produced horizontally oriented decoration like reeding, fluting, basket weave, and rhythmic patterns of incised squares and rectangles. The end (or crown) cam moved the axle of the lathe back and forth longitudinally, producing undulating patterns of curves and arches that moved vertically over the surface of the upright vessel. (5)

Inspired by the rose-and-crown engine-turning lathe he encountered on a visit to the Soho metal manufactory of Matthew Boulton (1728-1809) in Birmingham, in 1763, Wedgwood originally adapted the new technology to cut reeds, flutes, and shallow-incised decoration into the bodies of his red stoneware, black basalt, and multicolored jasper ware. The subsequent application of the engine-turning lathe to slip decoration resulted in the mechanization of two age-old slip techniques--inlay and sgraffito.