Soft-paste porcelain
They were called "soft paste" (after the French "pâte tendre") either because the material is softer in the kiln, and prone to "slump", or their firing temperatures are lower compared with hard-paste porcelain,[5] or, more likely, because the finished products actually are far softer than hard-paste, and early versions were much easier to scratch or break, as well as being prone to shatter when hot liquid was suddenly poured into them.
[7] The other European countries had much longer to wait, but most factories eventually switched from soft to hard-paste, having discovered both the secret and a source of kaolin.
[9] There were early attempts by European potters to replicate Chinese porcelain when its composition was little understood and its constituents were not widely available in the West.
Pastes with more clay (now more commonly referred to as "bodies"), such as electrical porcelain, are extremely plastic and can be shaped by methods such as jolleying and turning.
Soft-paste is fired at lower temperatures than hard-paste porcelain, typically around 1100 °C[14][15] for the frit based compositions and 1200 to 1250 °C for those using feldspars or nepheline syenites as the primary flux.
The lower firing temperature gives artists and manufacturers some benefits, including a wider palette of colours for decoration and reduced fuel consumption.
According to one expert, with a background in chemistry, "The definition of porcelain and its soft-paste and hard-paste varieties is fraught with misconceptions",[18] and various categories based on the analysis of the ingredients have been proposed instead.
[19] Some writers have proposed a "catch-all" category of "hybrid" porcelain, to include bone china and various "variant" bodies made at various times.
In 1702, letters-patent were granted to the family of Pierre Chicaneau, who were said to have improved upon the process discovered by him, and since 1693 to have made porcelain as "perfect as the Chinese".
It is rarely of a pure white, but the warm yellowish or ivory tone of the best wares of the period is sympathetic and by no means a shortcoming; and while actually very soft and glassy, it has a firm texture unlike any other.
The heavy build of the pieces is also characteristic and is saved from clumsiness by a finer sense of mass, revealed in the subtly graduated thickness of wall and a delicate shaping of edges.
A superior soft-paste was developed at Vincennes, whiter and freer of imperfections than any of its French rivals, which put Vincennes/Sèvres porcelain in the leading position in France and throughout the whole of Europe in the second half of the 18th century.
Remarkably little hard-paste porcelain has ever been made in England, and bone china remains the vast majority of English production to the present day.
It takes underglaze cobalt blue painting especially well, which is one of the factors leading it to be identified as the wares using a mineral ingredient called huashi, mentioned by Father François Xavier d'Entrecolles in his published letters describing Chinese production.
[46] Hard-paste porcelain was successfully produced at Meissen in 1708 by Ehrenfried Walther von Tschirnhaus, though Johann Friedrich Böttger who continued his work has often been credited with the discovery of this recipe.
As the recipe was kept secret, experiments continued elsewhere, mixing glass materials (fused and ground into a frit) with clay or other substances to give whiteness and a degree of plasticity.
