BASIC FACTS ABOUT PORCELAIN AND POTTERY

By Rebecca Markman, ISA CAPP, AM  © 2007

Porcelain, a ceramic ware originating in Asia centuries ago, is essentially made of clay.  Hard paste or “true” porcelain contains quartz and two types of decomposed granite, known as kaolin (china clay) and petuntse (china stone).   It vitrifies (turns into glass by heat and fusion) during the second (“glaze”) firing.  It is translucent and delicate but also strong.  Europeans strove to imitate Chinese porcelain using various soft paste formulas, often containing crushed glass but no kaolin, until a hard paste recipe was developed at Meissen in the early 18th century.   Prior to this discovery, a thriving china trade between Asia and Europe flourished for at least 125 years.  Ceramic items can be formed when modeled by hand, press-molded by machine, or slip cast.  Pre-fired decoration can be applied (raised), incised (cut), painted, stamped, and reticulated (pierced), in addition to other techniques.  Fired, unglazed porcelain is called bisque.  The liquid glaze (a thin layer of glass often mixed with powdered minerals and water) coating, whether transparent, opaque, white or colored, is then added and the piece is fired at a high temperature.  Glaze functions as waterproofing and can also act as colored decoration.   Over- glaze decoration can be colored paint or enamel, luster (a metallic oxide), gilding, transfer printing, or applied clay.  Some of these techniques require an additional firing.  Firing can cause cracking or crazing (a network of fine surface cracks) to the porcelain, resulting in lost production.  Porcelain manufacture is a highly honed skill.  Items popular for collectors include figurines, tableware, and vessels.

Pottery is a ceramic ware made essentially of clay and water and fired at much lower temperatures than porcelain.  Stoneware, earthenware, faience and majolica are all types of pottery.  Some companies, such as Minton and Wedgwood produced both porcelain and pottery wares.  Together, the combined categories of porcelain and pottery are called ceramics.

A short list of important 18th and 19th century Western ceramic manufacturers includes Belleek, Derby, KPM, Meissen, Minton, Sevrès, Vincennes, Wedgwood, and Worcester.  Items produced in the 18th century in good condition are typically more coveted than pieces made in the 19th century.  Many 20th century American potteries are known for their Art pottery wares, and such names as Fulper, Grueby, Newcomb, Ohr, Rookwood, Roseville, and Van Briggle have an avid collector base.

Basic facts about care and handling of porcelain: breakage, cracks and chips are the most common forms of damage to ceramic wares.  Therefore, care must be taken when handling, using, or displaying these items.  Dirt and dust can be gently wiped away with a soft dry or damp cloth.  Unglazed ceramics should only be dusted, because they are porous and water can cause staining.  Ceramics should not be subjected to extremes of temperature from the dishwasher, refrigerator, oven or sink; this can cause cracking.  If an item has crazing, it should not come into contact with liquid because staining or discoloration can occur. 

Rebecca Markman, ISA CAPP, AM  is a certified personal property appraiser specializing in 18th, 19th and 20th century American, British and European antique furniture, tableware, silver, glass, porcelain, pottery and paintings.