Types of Antique Ceramic , Earthenware,
Stoneware and Porcelain.
 There
are three main types of ceramic material -- coarse grained earthenware
and harder stoneware that go to make pottery, and the more delicate
and fine grained material collectively referred to as porcelain.
Earthenware :
Is coarse sedimentary clay which contains many impurities and can
only be fired to around 800°C. when fired the grains of the
clay stick together to form a hard structure with tiny air gaps
throughout. The gaps allow water or moisture to soak through the
structure and this means earthenware must be glazed if it is to
be used to hold water. The clays come in many colours which can
only be seen if a transparent glaze is used. Colour can usually
denote the origin of the clay. Torquay ware uses rusty orange and
iron rich Devon clays. Creamware
uses good quality white Devon clay which can be fired at higher
temperatures.
Stoneware :
Is harder than earthenware and has a finer texture. It can hold
water when unglazed. Stoneware clays can be fired to around 1300°C.
Most clays are grey and coloured stoneware objects usually only
have a skin of colour. However, chinese yixing
stoneware is red all the way through. Black basaltes and jasperware
are forms of fine stoneware first produced by wedgwood
in the mid-18thC.
Porcelain :
Was first produced by the Chinese in their late Tang dynasty over
1000 years ago. True, hard-paste porcelain is watertight when glazed
or unglazed. Porcelain can be white, grey or creamy and it is strong,
delicate and usually translucent. Meissen
produced the first true competitor to chinese porcelain in 1708.
Porcelain can be fired at over 1400°C and the higher the firing
temperature the better the ceramic paste changes into an impermeable
glassy body. Porcelain is usually hard to scratch. A soft-paste
porcelain was produced in Europe in the 16thC, it fired at 1100-1200°C
and was developed by adding glass, flint, quartz or bone (bone china)
to the clay.
Western porcelain is generally divided into the
three main categories of hard-paste, soft-paste and bone china,
depending on the composition of the paste (the paste is the material
used to form the body of a piece of porcelain).
Hard paste porcelain :
One of the earliest European porcelains was produced at the Meissen
factory and was compounded from china clay kaolin, quartz and alabaster
and was fired at temperatures in excess of 1350-degrees Celsius
to produce a porcelain of great hardness and strength. At a later
date the composition of Meissen hard paste was changed and the alabaster
was replaced by feldspar, lowering the firing temperature required.
China clay, feldspar and quartz (or other forms of
silica) continue to this day to provide the basic ingredients for
most continental European hard paste porcelains.
Soft paste porcelain :
Its history dates from the early attempts by European potters to
replicate Chinese porcelain by using mixtures of china clay and
ground-up glass or frit; soapstone and lime were known to have also
been included in some compositions. As these early formulations
suffered from high pyroplastic deformation, or slumping in the kiln
at raised temperature, they were uneconomic to produce. Formulations
were later developed based on kaolin, quartz, feldspars, nepheline
syenite and other feldspathic rocks. These were technically superior
and continue in production.
Bone China :
Although originally developed in England to compete with imported
porcelain, bone china is now made worldwide.
It has been suggested that a misunderstanding of an
account of porcelain manufacture in China given by a Jesuit missionary
was responsible for the first attempts to use bone-ash as an ingredient
of Western porcelain.
In China, china clay
was sometimes described as forming the bones of the paste, while
the flesh was provided by refined porcelain stone.
For whatever reason, when it was first tried it was
found that adding bone-ash to the paste produced a white, strong,
translucent porcelain.
Traditionally English bone china was made from two
parts of bone-ash, one part of china clay kaolin and one part of
Cornish china stone (a feldspathic rock), although this has largely
been replaced by feldspars from non-UK sources
The base and trade marks on antique pottery and porcelain.
Ceramic marks are applied in four basic ways: incised, impressed,
painted, printed
Incised or Impressed marks
The incised mark is applied by hand after making the basic model
in china clay and before the first firing at about 900 °C (biscuit
firing). The clay is still soft and this makes it easy to apply
the mark.
Impressed marks follow the same procedure, but the mark will be
stamped into the clay. This method is sometimes used to identify
undecorated white porcelain or white blanks.
Underglaze marks
The underglaze mark is a handpainted or printed mark that is applied
after the biscuit firing but before the glaze is applied.
Metal oxides are used that are resistant to the high kiln temperatures
of the glaze-firing proces (about 1400 to 1450 °C). Cobalt is
the most commonly used metal oxide and it gives an underglaze blue
mark.
Overglaze marks
The overglaze mark is a handpainted or printed mark that is applied
after the glaze firing and before the final firing. Painted marks,
usually name or initial marks, are added over the glaze at the time
of ornamentation, as were some stencilled marks.
Painted marks also use metal oxides that can be used during the
final firing which is not as high as the glaze firing process (about
800 °C). You will find overglaze marks in different colours,
however red (iron oxide) and green (copper oxide) are used most.
Gold can also be used, but the temperature in the kiln durng the
final firing process cannot exceed 400 °C. Overglaze marks are
used by painters and decorators on previously glaze fired objects.
Ceramic glazes.
A glaze is a glossy or glassy film that is fused to the ceramic
body during firing. It is usually formed from powdered minerals
added to water and washed or painted over the object. A glaze can
be shiny or matt, hard or soft
After application, the ceramic is fired, and the powdered coating
melts into a hard, glass-like coating. A ceramic glaze is usually
for decoration or protection and most glazes can be considered specialised
forms of glass.
Glazing is functionally important for earthenware vessels, which
without it would be unsuitable for holding liquids. In addition
to the functional aspects, aesthetic forms include a smooth pleasing
surface, the degree of gloss and variegation, and finished color.
Ceramic glazes can also enhance an underlying design or texture
which can be the natural texture of the clay or an inscribed, carved
or painted design.
Liquid glazes
Can be applied by dipping pieces directly into the glaze, pouring
the glaze over the piece, spraying it onto the piece with an airbrush
or similar tool, with a brush, or with any tool that will achieve
a desired effect.
To prevent a glazed article sticking to the kiln during firing
either a small part of the item is left unglazed or special supports,
kiln spurs, are used then removed and discarded after the firing.
Small marks left by these spurs can sometimes be visible on finished
items. Good early antique derby
porcelain figures without base marks can usually be identified
by the three pad marks left by the supports derby used during the
firing.
Early earthenware glazes were usually
based on lead and tin, which produced an opaque white finish. Early
soft-paste porcelain has a colourless lead glaze, but later soft-paste
porcelain had crushed flint or glass added to the glaze.
Lead glazes
were used until the 19th century when less dangerous materials were
found.
Tin glaze :
chips easily but provides a white ground that was perfect for colour
decoration .... more
Salt glaze
Stoneware has an orange peel effect produced by throwing salt into
the kiln during firing.
Crackle glaze, cracklure or crazing
occurs when the ceramic body and the glaze shrink at different rates,
as they cool. A crackle glaze is highly desriable on some items;
particularly Japanese Satsuma wares.
The types of decoration on antique ceramics.
Decoration on antique pottery and porcelain is usually either underglaze
or overglaze and painted or printed. Sometimes the glaze may form
the only decoration.
Overglazed decoration
Is when a layer of decoration is added on top of the glaze, usually
before it is fired. The colour borders can usually be seen on close
inspection or felt with the fingertips.
Overglaze colours on porcelain were usually applied using enamel
paints, because of the variety avaliable and as they did not have
to withstand the very high firing temperatures. Different enamels
were applied based on their firing temperatures, with the highest
applied first and gilding fired last.
Underglazed decoration
Is when pigment is applied to either an unfired or biscuit fired
piece of pottery before being coated with the glaze.
 The
pigment fuses with the glaze when the piece is fired, either for
the first time or during the glost firing.
The design pigment applied would be a metal oxide such as cobalt,
chromium, manganese or iron. When fired the oxide produces a colour
that appears to come from within the body of the ceramic. A good
example of underglaze decoration is the popular "blue and white"
porcelain where the blue colour is produced by using a cobalt pigment.
Copper pigment produces green or red, iron produces red and manganese
produces purple.
To test for underglaze or overglaze colour
- Hold the item so that sunlight falls across the pattern.
If the light obscures the pattern then the pattern is under the
glaze.
 Pate-sur-Pate
: Is where porcelain paste is built up in layers against a constrasting
colour ground to produce a piece that resembles cameo glass as the
meissen wall plaque on the right.
Both meissen and minton are famous for
the quality and excellence of their pate-sur-pate decoration and
their pate-sur-pate products are among the rarest and most expensive
pieces to come to the market in the modern age.
Reticulation - Is produced by piercing
the still soft clay with a variety of different tools to produce
an intricate latticework effect or pattern, before firing the object.
 Sprigging
- Is when moulded or stamped clay in decorative shapes are stuck
onto the object with thin slip before the firing.
The decorative shapes are usually in the form of sprigs of flowers
or leaves.
Wedgwood are famous for their classical sprigs on jasper ware.
As the Ulysses sprig by William Hoffman on the left.
Trailed Slip - Is created by dipping
the object in pale slip then trailing various colours of slip on
top of it in intricate patterns.
Staffordshire trailed slip - Is a
thin, buff-bodied earthenware coated with white and dark slips and
decorated with trailed, combed, or marbled designs.
Generally, the white slip covers more of the visible surface than
the dark slip. A clear lead glaze gives the piece a yellowish background
color. Sometimes the visible light and dark slip are reversed, producing
a brown vessel with yellow decoration.
Slipware was made in the Staffordshire region by the mid-17th century
and the first well known Staffordshire slipware products were the
elaborately decorated ornamental dishes and chargers popularly called
Toft Ware, after the Toft family of potters.
They were in production by around 1660, and continued to be made
into the 1720s............... more
 Sgraffito
or sgraffiato :
Is produced when the object is dipped in a coloured slip and the
artist then carves patterns in the slip to reveal the constrasting
coloured ground beneath.
Doultons, Hannah Barlow
is one of the most sought after sgraffito artists, famous for her
naturalistic animal scenes on Doulton
Lambeth stonewares.
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There are vastly more antique objects made of pottery, porcelain, earthenware
or stoneware than of any other material and you probably have some
beautiful antique ceramics in your home. You are more likely to
possess antique pottery and porcelain than you are antique silver,
glass or furniture. 