Soft-paste porcelain

Soft-paste porcelain is a type of a ceramic material, sometimes referred to simply as "soft paste". The term is used to describe soft porcelains such as bone china, Seger porcelain, vitreous porcelain, new Sèvres porcelain, Parian porcelain and soft feldspathic porcelain, and is also used more narrowly to describe clay bodies mixed with glass frit, used mainly in the production of decorative figures and domestic wares in 18th century Europe. The porcelain was termed "soft" because of their lower firing temperates compared with hard-paste porcelain.

The history of soft-paste porcelain dates back to early attempts by European potters to replicate Chinese porcelain at a time when its composition was little understood and its constituent materials were not widely available in the West. The earliest formulations were mixtures of clay and ground-up glass (frit). Soapstone and lime are also known to have been included in some compositions.

Medici porcelain was the first successful attempt in Europe to make imitations of Chinese porcelain. Produced between 1575 and 1587 the body is a type of soft-paste porcelain, composed of white clay containing powdered feldspar, calcium phosphate and wollastonite (CaSiO3), with quartz.

Other early European soft-paste porcelain, also a frit porcelain, was produced at the Rouen manufactory in 1673, which was known for this reason as "Porcelaine française". Again, these were developed in an effort to imitate high-valued Chinese hard-paste porcelain.

As these early formulations suffered from high pyroplastic deformation, or slumping in the kiln at raised temperatures, they were difficult and uneconomic to use in mass. Formulations were later developed based on kaolin (china clay), quartz, feldspars, nepheline syenite, and other feldspathic rocks. Soft-paste porcelain with these ingredients was technically superior to the traditional soft-paste and these formulations remain in production.

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Wikipedia