Semi-porcelain is commonly referred to as “ironstone,” but it also goes by other names. Though the fired clay body does appear somewhat vitreous (glass-like), it is actually a refined earthenware and not to be confused with true porcelain.
Differences from Porcelain
Porcelain clay is fired at temperatures above 1,300 degrees Celsius, and semi-porcelain, made from earthenware clay, is fired at around 1,200 degrees Celsius. A broken edge of semi-porcelain can be readily distinguished from porcelain.
Origins of Semi-Porcelain
In the early 19th century, English Staffordshire potteries began experimenting with a porcelain-like ware that could be cheaply mass-produced. Charles Mason patented this new ware in 1813, which he called “Ironstone China.”
Staffordshire is the historic center of semi-porcelain (ironstone) production. By the mid-1800s, several Staffordshire potters produced ironstone because of the presence of high-quality clay within the district.
Americans quickly became consumers of semi-porcelain. After the Civil War, Ohio and New Jersey became the center of production in the U.S.
Semi-porcelain dishes are heavier and thicker than their porcelain counterparts (porcelain dishes are thin). Look for the terms, “semi porcelain,” “ironstone china,” “semi-vitreous porcelain,” “English porcelain” or other similar names on the maker’s mark.
John Peterson published his first article in 1992. Having written extensively on North American archaeology and material culture, he has contributed to various archaeological journals and publications. Peterson has a Bachelor of Arts from Eastern New Mexico University and a Master of Arts from the University of Nebraska, both in anthropology, as well as a Bachelor of Arts in history from Columbia College.