Fact Check: What Are The Primary Types of Porcelain?

By: blog.RubyLane.com

There are two primary types of Porcelain, with a third distinguished by nomenclature when a specific additive to a basic formula is included:

Hard Paste Porcelain
The formula to make hard paste porcelain includes two essential ingredients, china clay (kaolin) and china stone (petuntse) which are both decomposed forms of granite. During the firing process, which is done at very high temperatures, actual bonding of clay particles occurs, which vitrifies the body to a glass-like consistency.

Distinguishing characteristics of hard paste porcelain are translucency (light shows through the body), impermeability, and a resonant sound when tapped. Because a hard paste porcelain glaze fuses with the body at firing, rather than resting like a separate skin on the outside surface, as do pottery glazes, hard paste porcelain that has not been flawed in some way at manufacture will not exhibit glaze crazing. Chips will be shell-like and inside an area of damage the body looks shiny. Though extremely resilient, porcelain has a brittle structure and when broken shatters into glassy fragments, rather than into rough chunks or pieces like pottery.

Bisque or Biscuit and Parian are also types of hard paste porcelain, with the number of firings or a lack of surface glaze distinguishing them from glazed porcelain products.

Soft Paste Porcelain
In trying to discover how to produce hard paste porcelain, different soft paste porcelain formulas were instead developed by porcelain makers outside of China, with each variously combining fine clay with either frit (powdered glass), soapstone or bone-ash. Soft paste porcelain was fired at a lower temperature than hard paste and so a wider variety of colors could be used in its decoration.

Distinguishing characteristics of soft paste include translucency, but translucency may not always seem entirely consistent. There may be patches within that seem thin, or more translucent, when a piece is held to the light. Chipped soft paste porcelain exhibits a granular interior, rather than one that is glassy. Generally not as stable in firing, soft paste items often may exhibit production issues like fire-cracks. The glaze of soft paste is not fused to the body in the same manner as hard paste, but remains on the surface, thus some early soft paste items may exhibit crazing. Soft paste is less resilient than hard paste and its glaze can be scratched more easily. Glaze also tends to ‘pool’ in places like the crevices of figurines or the interiors of foot-rims.

Due to production issues, cost, and other shortcomings in comparison to the production of hard paste porcelain, once the formula for making hard paste became widely known the manufacture of soft paste was dropped by the wayside. Production of it had mostly ended by the first quarter of the 19th century.

Manufacturers who made articles in soft paste porcelain included Chantilly, Vincennes and Sevres, in France; Chelsea, Worcester and Bow in England; and John Bartlam in America, who is credited with producing the first soft paste porcelain, a type of Queensware, in America after about 1765. Bartlam employed workers who previously had worked in English potteries before coming to America in his South Carolina works, to the great chagrin of one English potter in particular, Josiah Wedgwood.

Bone China
This type of porcelain is a hybrid similar in make-up to hard paste porcelain but also containing large amounts (45% to 50%, or so) of bone-ash in addition to china clay and stone. First created in England ca. 1795, the body of bone china ware is very strong, white, translucent and resistant to thermal shock. Distinguishing characteristics for it are the same as those given for hard paste porcelain.

Well known Bone China manufacturers include Spode, Derby, Coalport and Minton.

In ceramics the term ‘china’ should only be used professionally to describe hard paste porcelain articles made in China, to describe similar Western objects made in the manner of Chinese porcelain, or in reference to ‘Bone China.’ It is technically incorrect to call an item made of a type of pottery ‘china.’

Article Source: https://www.collectibles-articles.com

Source: Notes from the Lane at blog.rubylane.com - Your complete resource for online sales success. RubyLane.com is home to over 2000 online shops from around the world offering Antiques and Art, Vintage Collectibles and Jewelry in 2,000 categories.

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