Bone ash in the context of Opacifier

Soft-paste porcelain (sometimes simply "soft paste", or "artificial porcelain") is a type of ceramic material in pottery, usually accepted as a type of porcelain. It is weaker than "true" hard-paste porcelain, and does not require either its high firing temperatures or special mineral ingredients. There are many types, using a range of materials. The material originated in the attempts by many European potters to replicate hard-paste Chinese export porcelain, especially in the 18th century, and the best versions match hard-paste in whiteness and translucency, but not in strength. But the look and feel of the material can be highly attractive, and it can take painted decoration very well.

The ingredients varied considerably, but always included clay, often ball clay, and often ground glass, bone ash, soapstone (steatite), flint, and quartz. They rarely included the key ingredients necessary for hard-paste, china clay including kaolin, or the English china stone, although some manufacturers included one or other of these, but failed to get their kilns up to a hard-paste firing temperature. 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, 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.

Bone china is a type of vitreous, translucent pottery, the raw materials for which include bone ash, feldspathic material and kaolin. It has been defined as "ware with a translucent body" containing a minimum of 30% of phosphate derived from calcined animal bone or calcium phosphate. Bone china is amongst the strongest of whiteware ceramics, and is known for its high levels of whiteness and translucency. Its high strength allows it to be produced in thinner cross-sections than other types of whiteware. Like stoneware, it is vitrified, but is translucent due to differing mineral properties.

In the mid-18th century, English potters had not succeeded in making hard-paste porcelain (as made in East Asia and Meissen porcelain), but found bone ash a useful addition to their soft-paste porcelain mixtures. This became standard at the Bow porcelain factory in London (operating from around 1747), and spread to some other English factories. The modern product was developed by the Staffordshire potter Josiah Spode in the early 1790s. Spode included kaolin, so his formula, sometimes called "Staffordshire bone-porcelain", was effectively hard-paste, but stronger, and versions were adopted by all the major English factories by around 1815.

The Bow porcelain factory (active c. 1747–64 and closed in 1776) was an emulative rival of the Chelsea porcelain factory in the manufacture of early soft-paste porcelain in Great Britain. The two London factories were the first in England. It was originally located near Bow, in what is now the London Borough of Tower Hamlets, but by 1749 it had moved to "New Canton", sited east of the River Lea, and then in Essex, now in the London Borough of Newham.

Designs imitated imported Chinese and Japanese porcelains and the wares being produced at Chelsea, at the other end of London. From about 1753, Meissen figures were copied, both directly and indirectly through Chelsea. Quality was notoriously uneven; the warm, creamy body of Bow porcelains is glassy and the glaze tends towards ivory. The paste included bone ash, and Bow figures were made by pressing the paste into moulds, rather than the slipcasting used at Chelsea. Bow appears to have been the largest English factory of its period. After about 1760, quality declined, as more English factories opened, and the dependence on Chelsea models increased, perhaps aided by an influx of Chelsea workers after 1763, as production there decreased.