Soft Paste Porcelain
Soft paste porcelains were made in England, Continental Europe and the United States, in imitation of Chinese porcelain. English soft paste porcelain from the 18th century has a somewhat softer paste than Chinese hard paste porcelain and a clear, semi-gloss glaze that frequently appears distinct from the body. The glazed surface of soft paste porcelain fluoresces a dull pink to greyish purple under shortwave and mid-range ultraviolet light.
English soft paste porcelain was first successfully made as early as the mid-1740s (Owen 2007) and was present in many American households in the third quarter of the eighteenth century (Jellicoe and Hunter 2007:166). Nevertheless, it generally forms a small percentage of porcelain recovered from archaeological contexts in the United States. The majority of English soft paste porcelain found archaeologically is from the Bow Factory in London, as well as from manufacturers in Liverpool (Jellicoe and Hunter 2007:168).
Experimentation to produce porcelain in America occurred late in the 18th century. In Philadelphia, the American China Manufactory of Gouse Bonnin and George Anthony Morris was in operation between 1770 and 1772 (Hood 2007). In South Carolina, John Bartlam was producing soft paste porcelain as early as 1765, continuing to 1770 (Hudgins 2009). Distinguishing between North American and English soft paste porcelain will generally be difficult unless the sherd is marked or the vessel is nearly complete. The development of bone china in the 1790s was largely responsible for the demise of soft paste porcelain production by the early 19th century.
Soft paste porcelain has also been called “artificial” or “glass-frit” porcelain, since powdered “frit” (pulverized glass) was sometimes substituted for the kaolin used by the Chinese in their porcelain (Cushion and Cushion 1992:13; The Potteries 2016). Various paste recipes, however, were used by different factories as they tried to improve the quality and appearance of their wares, as well as minimize loss of vessels during firing (Owen 2007). English soft paste porcelains were composed of white clay combined with various ingredients, including lime, chalk, small amounts of sand, gypsum, soda, soapstone, bone ash, salt and even recycled, ground Chinese porcelain (Cushion and Cushion 1992; the Potteries 2016). Using results of petrological analysis of English and American soft paste porcelain, J. Victor Owen (2007) proposed a classification scheme for soft paste porcelains based on the chemical composition of pastes.
English soft paste porcelain generally has a dense and ‘chalky’ paste that is slightly more porous and softer than its Chinese counterpart. Soft paste sherds can become discolored or stained around cracks or from contact with soil. The paste, which scratches easily with a steel file, often has a greyish hue, sometimes with surface black specks (Hughes 1968:39). According to Miller and Stone (1970:90), English soft paste shows a granular fracture under magnification, while hard paste has conchoidal fractures. Like other porcelain, soft paste is translucent, although some later underfired pieces by the Bow factory can be opaque (Cushion and Cushion 1992:13).
Underglaze decorated English soft paste porcelain is fired twice; first at a higher temperature (1100 C – 1250 degrees C) to create the unglazed biscuit ware and then at a lower temperature (1050 C - 1150 degrees C) for the glaze (Ramsay and Ramsay 2008). In addition to being fired at lower temperatures than hard paste porcelain, soft paste porcelain was fired for a shorter time.
The clear semi-gloss glaze on English soft paste porcelains was made from various recipes, but usually contains lead (Kingery 1986; Owen 2002). The glaze is generally distinct from the paste in cross section and visible as a thin white line along each surface. It sometimes gathers in pools in vessel foot rings and, unlike hard paste porcelain vessels, the foot rings of soft paste porcelain vessels are glazed. Also unlike hard paste porcelain, soft paste glaze will often be crazed and show scratching from cutlery (Cushion and Cushion 1992:16). The glazed surface of soft paste porcelain fluoresces a dull pink to greyish purple under shortwave and mid-range ultraviolet light.
English wares were decorated in painted and printed motifs under the glaze in blue, and with overglaze enamels in painted and transfer printed patterns. Overglaze enamels were often added to a transfer printed design, and gold gilding was also added as a decorative element. The most commonly-found English soft paste porcelains in North American archaeological contexts tend to be decorated in blue and white. Design motifs included Chinese-style landscape and floral patterns (willow trees, rocks, peonies and temples) as well as floral patterns in the Meissen style (Fisher 1968:10). Since English soft paste porcelain was often produced through slip casting or press molding, molded decorations are also common.
Soft paste porcelain was produced in a variety of tea, table and decorative vessels, but the majority of what is found archaeologically in North America has a more limited range of forms, including cups, saucers, tankards, teapots, sauceboats and plates.
Cushion and Cushion 1992; Fisher 1968; Hood 2007; Hudgins 2009; Hughes 1968; Jellicoe and Hunter 2007; Kingery 1986; Miller and Stone 1970; Owen 2002; 2007; The Potteries 2016; Ramsay and Ramsay 2008