Soft porcelain differs from hard porcelain in a smaller amount of kaolin and clay in the composition. Instead, the content of other substances, mainly vitreous additives, has been increased. This is quartz sand, saltpeter, sea salt, alabaster or something else – the chemical composition is diverse. This type of ceramics got its name because more liquid phase is formed during firing, which increases the risk of deformation of the workpiece. Already during the melting process, gypsum and clay are added to the vitreous mass.
Glaze also consists mainly of glass. After its application, the products are fired again, and the glaze is fused with the shard. The firing temperature is lower than that of solid materials. Usually + 1300-1350 ° C is sufficient.
Soft porcelain is more transparent than hard porcelain. It has a beautiful white or creamy shade. The ringing from a blow with a wooden stick is more melodic. But impact resistance and heat resistance are reduced by about half.
Here are some of the characteristics that distinguish soft porcelain:
- in the places of the chip, the granular structure of the unglazed surface is noticeable;
- areas without glaze can become dirty or discolored over time;
- if you run a knife over the glaze, a scratch will remain; antique items made from this material are usually more cracked.
Soft porcelain: a story of origin
Soft porcelain appeared in Europe a century and a half earlier than hard porcelain. It was first opened in Florence at the Medici family manufactory, this happened in 1575-1587. But this type of pottery was imperfect, and its production was economically unprofitable. Better recipes have been found in France in an attempt to replace expensive Chinese porcelain.
In 1673, a small Rouen manufactory in Normandy found a formula that other factories later adopted. The owner and master of the production was Louis Potter. His products were famous for their whiteness and cobalt painting. In addition to blue paint, red and green were used. The dishes were painted over the glaze and burned, no stamps were put. The merit of Louis Potter also lies in the fact that he was the first to stop imitating the oriental masters by inventing painting in the original French style.
soft porcelain began to be produced in other places in France
Soon, soft porcelain began to be produced in other places in France: in Passy near Paris, Chantilly and Saint-Cloud. Basically, factories were engaged in imitation of Chinese and Japanese designs. Original French motifs appeared in the products of the Vincennes Porcelain Manufactory in the later period.
After 1756, the Vincennes factory moved to new buildings in Sevres. This is how the history of the beautiful and highly valued products of the Sevres Manufactory began. For a long time, she was patronized by the Marquise de Pompadour, after whom the rare pink color used in dyeing was named. Soft porcelain continued to be produced after the discovery of hard porcelain, because it was cheaper and perfectly suited for artistic products.
In England, the production of soft porcelain began a little later. The technology of making soft porcelain mass came to the island together with the Huguenots who fled from France. In 1749, Thomas Briand presented the first samples to the Royal Society of London, similar to the products of the Saint-Cloud manufactory. Then the Royal Worcester factory and other representatives of the porcelain industry in England worked with such ceramics.
Application of soft porcelain
Despite its low strength, soft porcelain is still in demand today. It is fired at lower temperatures, which leaves more room for coloring. When firing hard porcelain for underglaze painting, dyes based on cobalt, chromium and iron can be used, while other compositions are discolored.
A soft mass with a lower melting point allows the use of delicate and varied tones. It is also easier for the soft mass to form a complex shape. It is used to make figurines, interior items with gracefully curved shapes and thinner dishes. This material is ideal for artwork or special occasion crockery.