Chemistry Reference
In-Depth Information
and
faience
were used to refer to glazed earthenware made in the Spanish
island of Majorca and Faenza in Italy, respectively. At present, however,
the names refer to two different varieties of relatively coarse earthenware
made in many places, which is generally red or gray, has a porosity of
about 15%, and is therefore mostly opaque. To add to the confusion, in
archaeology the term
faience
is also associated with a material used mainly
in Egypt:
Egyptian faience
(see text below) which is made not from clay but
from quartz.
Stoneware
Stoneware
is the term commonly used to refer to a very strong ceramic mate-
rial that is fired at a high temperature (1200°C-1300°C, the highest temper-
ature attainable in most ancient kilns). The high temperature causes quite
extensive vitrification and relatively low porosity (generally below 5%),
although not sufficiently low to make it translucent. Stoneware is therefore
opaque to visible light. Stoneware objects may be of a variety of colors,
ranging from gray through cream and brown to red. Its surface may be either
glazed or unglazed. Stoneware was probably first made in China during the
seventh century C.E. In Europe, distinctive stoneware objects seem to have
been made only since the late fourteenth century C.E., initially in Flanders
(Belgium) and Germany.
Porcelain
Most if not all ancient terracotta and earthenware, and some stoneware, are
made from secondary clay.
Porcelain
, the strongest ceramic material known
until the twentieth century has always been made from primary clay, kaolin,
also known as
China clay
. The clay paste used for making porcelain consists
of a mixture of kaolin and a type of feldspar known in China as
penutse
and
in the West as
China stone
; formed porcelain objects are fired at very high
temperatures, about 1300°C and higher. Some Chinese porcelain includes
also a third mineral such as mica, which varies in different geographic
regions and yields characteristic local varieties of porcelain. The extremely
high firing temperature results in a high degree of vitrification and conse-
quently a very low porosity (below 2%), which makes porcelain highly
translucent. Since the kaolin and feldspar used contain few impurities,
porcelain is white. When struck, porcelain produces a prolonged sound
(Maneta 1997; Yap and Hua 1994, 1992).
