A General Overview of Ceramics and Glazes
Identifying an object as a ceramic simply means the object was made, at least in part, with clay.
Clay minerals are hydrous aluminum phyllosilicates with variable amounts of iron, magnesium, alkali metals (lithium, sodium, potassium, rubidium, cesium, and francium), and alkaline earths (beryllium, magnesium, calcium, strontium, barium, and radium.)
Not all clays are alike. Just as there are endless varieties of rocks and minerals on earth, there are endless varieties of clay. Specific elements and minerals in clay deposits will determine heat tolerance and other variables that make some clays a superior choice for certain types of ceramics.
It cannot be overstated that ceramics play an important role in archaeology and the quest for knowledge of early civilizations.
In general, all ceramics fall into three broad categories: earthenware, stoneware, and porcelain.
EARTHENWARE
Objects made from clay fired at a lower heat, earthenware is more susceptible to breaking and chipping versus the more durable stoneware and porcelain. Unless glazed, earthenware is porous and cannot hold liquids.
Unfired earthenware is greenware.
First firing to biscuit 850 – 1100 C.
Types of Earthenware
Alkaline glaze (Ash) – Archaeologists have unearthed ash-glazed shards they believe were accidently glazed by falling ash from a wood fire. These shards date from 1500 BC in China. By 1000 BC, Shang dynasty potters intentionally added ash glaze to earthenware. Prior to c. 800 AD, Mesopotamian pottery used alkaline-glazed earthenware for domestic needs.
Creamware – Cream-colored earthenware with a transparent lead glaze. Examples include: Queen’s Ware and Pearlware (a refined creamware, with cobalt (blue) in glaze as whitener.)
Lead glaze – First developed in the Near East in c. 2000 BC, lead glazes sealed earthenware making it nonporous. Chinese Han dynasty potters (206 BC – 220 AD) used both clear and colored lead glaze for utilitarian and decorative purposes. The Tang dynasty (618 – 906 AD) is well known for earthenware (and stoneware) with tricolor (amber, green, and cream) Tang sancai associated with the ubiquitous Tang horse and tomb figures. Lead glaze easily fuses with metal-oxides for a variety of color and decorative effects.
English 18th c. earthenwares were often lead glazed with a multitude of decorative effects including:
- Agateware – Different colored clays worked together to imitate stone. Once potted, the objects were covered in a clear lead glaze.
- Blackware – Purplish-black body under a yellowish clear lead glaze or dark, reddish body under blackish-brown lead glaze (archaic: Jackfield Ware).
- Tortoiseshell ware – Different colored lead glazes create a mottled, shiny surface.
- Slipware – Mixture of clays and other minerals such as quartz, feldspar, and mica create a slip that is placed onto an unfired clay body surface by a variety of techniques including dipping, painting, piping, or splashing.
Tin glaze – A white, opaque glaze of tin oxide that is added to lead glaze. The earliest tin-glazed pottery appears near Bagdad in 9th c. The technique spread to Egypt, Persia, and Spain before reaching Italy, Holland, England, and France. Mesopotamian tin-glazed earthenware designs were influenced by the imported Tang ceramics beginning about 800 AD. Chipped or damaged tin-glazed earthenware will reveal a buff-colored clay beneath.
Tin-glazed earthenware is also referred to as:
- Delftware – Dutch pottery first made in the 1500’s in Antwerp by Italian potter Guido da Savino. Only capital “D” for tin-glazed earthenware made in Holland.
- English delftware – British pottery beginning in 1550’s. Galleyware (period term) was produced in London, Bristol, and Liverpool with smaller centers at Wincanton, Glasgow, and Dublin.
- Faience – French pottery dating from 1530’s in Rouen. During 17th c., both Rouen and Nevers faience was successful.
- Maiolica – Italian pottery dating from Renaissance era.
Redware. Red earthenware. (Same term sometimes used for red stoneware). Objects can be fired unglazed (biscuit) or fired with a clear lead glaze.
Lusterware – An iridescent metallic glaze. Glaze can be used on earthenware and other ceramic bodies. After a first firing, objects are covered in metallic glaze and fired a second time, at a lower temperature, in a muffle kiln.
STONEWARE
Objects made of clay that can withstand a higher firing threshold than earthenware, resulting in a more durable object.
Firing at 1200 – 1300 C.
Appears during the Chinese Shang dynasty (c. 1200 – 1046 BC).
After firing, stoneware is nonporous. Therefore, a glaze is not necessary to make objects utilitarian.
Any glazing that is done for decorative purposes, including a salt glaze, is done at the same time as the first firing.
Types of Stoneware
Alkaline glaze (Ash) – Calcium oxide, sometimes called quicklime, is a common alkaline glaze. Edgefield District, South Carolina in 19th c. developed a utilitarian pottery industry that included alkaline glaze. This tradition traveled with potters who moved to Texas in the 19th c. Some potters came to Texas as enslaved persons and after the Civil War owned successful pottery businesses.
Unglazed stoneware – Many different colors.
- Red –Yixing red clay was used in the Song dynasty (960–1279) to make stoneware teawares. The practice of tea drinking became popular among the Dutch nobility and wealthy merchant class beginning in the late 1660s and 1670s, creating demand for imported Chinese redware teapots (Yixing/I-Hsing teapot). The Dutch factory of Arij de Milde created domestically-made redwares. Dutch potters John and David Elers brought the style to Staffordshire, England in the 1690s.
- Black basaltes (iron oxide) – English potter Josiah Wedgwood began production at Etruria of a black stoneware body in 1768, creating forms inspired by antique originals from collections like Sir William Hamilton.
- Jasperware: blue (cobalt oxide), sage green (chromium oxide), lilac (manganese oxide), with yellow (salt of antimony.) Jasperware is sometimes referred to as “Wedgwood.”
- Caneware – A buff-colored stoneware body of marlstone, carbonate-rich clay and silt. Like black basaltes and jasperware, caneware was produced at Etruria by Josiah Wedgwood in 1770’s. Extremely fashionable during the Regency period (c. 1800-1820) and noted for use of bamboo motifs. Produced by Spode, Davenport, Elijah Mayer, Turner, and the Herculaneum factory.
Salt glaze – Clay can be white, buff to brown, or gray body. Salt, shoveled into the hot kiln, vaporizes. The sodium bonds with the clay’s silica to form orange-peel-like glaze. Chlorine escapes as poisonous gas.
Important discovery by German potters in 1300’s in Hessen and Rhineland areas.
Earliest English salt-glazed stoneware dates 1650–1700 in London. The similarity of the English salt-glazed wares to German products of the same design has led scholars to attribute the English wares to the work of German immigrant potters. Englishman John Dwight of Fulham Pottery obtained a patent for his pottery in 1671. English white salt-glazed stoneware was extremely popular in the 1770’s. In addition to the ash glaze, salt glaze was also used by potters in Edgefield District, SC and Texas in the 19th c.
Feldspathic glaze – Also referred to as a smear glaze. Chinese used feldspathic glaze as early as the Bronze Age (Shang dynasty c. 1200 BC).
- Yue ware – A fine, white stoneware that was produced in China during the Han dynasty (206 BC – 220 AD).
- Celadon – Glazes (olive or brownish green feldspathic glaze) used on stoneware in China and throughout Southeast Asia during Tang dynasty (618–907 CE). Celadon remains a popular glaze for stoneware for Chinese, Korean, and Japanese ceramics.
- Castleford-type – English feldspathic glazed stoneware, Castleford ware (1790-1820), was popular in England and exemplified a Neoclassical aesthetic.
PORCELAIN
Chinese Export and traditional hard-paste porcelain
Chinese made first porcelain during Han dynasty (196 BC – 220 AD)
Porcelain is made with two types of clay, kaolin and petuntse, and is coupled with a lime-based glaze.
Hard-paste is another term for porcelain.
Hard-paste porcelain is fired at 1450 C.
First European to discover recipe for porcelain (mixture of kaolin and petuntse clays) was Johann Friedrich Böttger in Saxony, Germany in 1709.
First commercially successful USA factory producing hard-paste porcelain is Tucker in Philadelphia, PA. (1826-1838.)
Bone china
A white translucent porcelain with a high quantity of bone ash.
Introduced about 1800 by Josiah Spode II, the formula is six parts bone ash, four parts china stone, and three and a half parts china clay; this formula is still used today. Bone china does not chip as easily as true, hard-paste porcelain.
Thomas Frye at his Bow porcelain factory in East London, 1748, is credited with the first successful bone china.
Josiah Spode in Stoke-on-Trent developed the concept between 1789 and 1793, introduced “Stoke China,” 1796. His son, Josiah II rechristened the ware bone china. Other manufacturers included: Minton, Coalport, Davenport, Royal Crown Derby, Royal Doulton, Wedgwood, and Worcester.
Biscuit / Parian porcelain
Unglazed, can be hard-paste or soft-paste porcelain.
Sometimes erroneously termed bisque in England and United States.
Pottery that has been fired once but not yet glazed. It is not necessary to glaze porcelain to make it nonporous.
Commercially introduced at Sevres, France in 1750’s for modeling figures and groups.
At the English Derby factory, the rule was only faultless wares were left biscuit.
The fashion of biscuit wares was revived in the 19th c., c. 1840’s. The period term for 19th c. biscuit porcelain is Parian.
The phrase “on the biscuit” is often used to refer to enamel decoration applied directly to biscuit as opposed to a previously applied glaze.
Soft-paste or Artificial porcelain
Does not contain feldspathic rock but instead usually ground glass.
Fired at 1200 C., a lower temperature than traditional Chinese porcelain.
Saint-Cloud – In 1702, Philippe I, Duke of Orléans gave letters-patent to the family of Pierre Chicaneau. A French factory in the city of St. Cloud, it was the first important French maker of soft-paste porcelain.
Thomas Briand of the Royal Society is credited with the first soft-paste porcelain in England in 1742. Early English potteries include: Chelsea (1743); Bow (1745); Longton Hall (1750); Royal Worcester (1751); Derby (1757); and Lowestoft (1757). The formula for this soft-paste porcelain was probably based on Saint-Cloud porcelain.
Colonial American Bonnin and Morris (American China Factory) was the first commercially successful soft-paste porcelain factory in Philadelphia, 1770 – 1772.
All soft-paste porcelain recipes lack kaolin and/or petuntse, ingredients that separate soft-paste porcelain from traditional Chinese porcelain.
Various glazes and methods of decoration are used on soft-paste porcelain, including hand painting, gilding, and transfer-printing.
WHITEWARE
The Exception – Sometimes called ironstone china, whiteware does not exactly fit into any of the three basic ceramic categories of earthenware, stoneware, and porcelain. Whiteware has some features of earthenware but because it may be fired at temperatures approaching stoneware, it is not an earthenware. The term Mason’s Ironstone derives its name from the British Staffordshire potter Charles James Mason. His patent of 1813 for whiteware become so popular with the public, British whiteware is known colloquially as Mason’s Ironstone.