white ware bowl, not tin-glazed (left), found in
Iran, and Iraqi tin-glazed earthenware bowl (right) found in
Iraq, both 9th–10th century.
British Museum. The earliest tin-glazed pottery appears to have been made in
Abbasid Iraq (750–1258) in the 8th century, fragments having been excavated during the First World War from the palace of
Samarra about fifty miles north of
Baghdad. The history of tin glazes in the Islamic world is disputed. One possible reason for the earlier production of tin-glazed wares could be attributed to the trade between the
Abbasid Empire and ancient China from the 8th to 9th century onwards, resulting in imitation of white Chinese
stoneware by local Islamic potters. Another might be local glaze-making rather than foreign influence, supported by the similarity between the chemical and microstructural features of pre-Islamic white opaque glazes and that on the first tin-opacified wares resulting in the emergence of Italian
Maiolica. Amongst others,
Luca della Robbia, born in Florence about 1400, used tin oxide as an opacifier in glazes. Potters began to draw polychrome paintings on the white opaque surface with metallic oxides such as cobalt oxide and to produce
lustreware. The off-white fired body of
Delftware and English
Majolica was made to appear white, and hence mimic the appearance of Chinese porcelain, by the application of a glaze opacified and coloured white by the addition of tin oxide. By the late 18th century the reduction in the price of
porcelain, and the new English
creamwares and related types, stronger, lighter and often cheaper than traditional earthenwares, hit the production of tin-glazed wares very hard, and production of "useful" rather than decorative wares almost ceased, so that "by 1850 the industry was almost extinct" in France. In 1947 Arthur Lane wrote it was "now only [made in Europe] in a few places to provide the tourist with souvenirs"
Manufacturing process and colours Though the recipe of tin glazes may differ in different sites and periods, the process of the production of tin glazes is similar. Generally speaking, the first step of the production of tin glazes is to mix tin and lead in order to form oxides, which was then added to a glaze matrix (alkali-silicate glaze, for example) and heated. After the mixture cooled, the tin oxide crystallises as what has been mentioned above, therefore generates the so-called white tin-opacified glazes. Besides, the body of tin-opacified wares is generally
calcareous clays containing 15-25% CaO, of which the
thermal expansion coefficient is close to that of tin glazes, thus avoid
crazing during the firing process. On the other hand, the calcareous clay fired in an oxidising atmosphere results in a buff colour, thus lower the concentration of tin oxide used The white opaque surface makes tin glaze a good base for painted decoration. The decoration is applied as metallic oxides, most commonly
cobalt oxide for blue,
copper oxide for green,
iron oxide for brown,
manganese dioxide for purple-brown and
antimony for yellow. Late Italian
maiolica blended oxides to produce detailed and realistic polychrome paintings, called
istoriato. To these oxides modern potters are able to add powdered ceramic colours made from combinations of oxide, sometimes
fritted. In the sixteenth century, the use of subtle and blended colours which were not strong enough to penetrate the opaque glaze made the delicate control of tonal values possible, and the painting therefore had to be done on the glaze surface, which then becomes a common manner of painting on tin-glazed wares. The disadvantage was that only a narrow group of pigments produced good colours after firing at the relatively high temperatures of up to . These included
cobalt blue,
manganese dark purple,
copper green,
antimony yellow, and the very tricky iron reds and brown, which only some potters were able to make as a good red. In the 18th century
overglaze enamels began to be used in the same way as on
porcelain; this technique is often called
petit feu in English when talking about faience (the Italian name is
piccolo fuoco). A much wider range of colours was possible, but after the fired and glazed wares were painted a third firing was required, at a lower temperature of perhaps . In modern versions, the pottery vessels are biscuit fired, usually between . The fired vessel is dipped in a liquid glaze
suspension which sticks to it, leaving a smooth and absorbent surface when dry. On this surface colours are applied by brush, the colours made from powered oxides mixed with water to a consistency of water-colour paint, sometimes with the addition of a binding agent such as
gum arabic. The unfired glaze absorbs the pigment like
fresco, making errors difficult to correct but preserving the brilliant colors of the oxides when fired. The glazed and decorated vessels are returned to the kiln for a second firing, usually between 1000 and 1120 °C (the higher temperatures used by modern potters). Lustered wares have a third firing at a lower temperature, necessitating a delicate control of the amount of oxygen in the kiln atmosphere and therefore a flame-burning kiln. Traditional kilns were wood firing, which required the pots to be protected in the glaze and luster firings by
saggars or to be fired in a
muffle kiln. Except for those making luster ware, modern tin-glaze potters use electric kilns. The recrystallisation of tin oxide during the firing provides evidence of the slightly different methods of different production sites, as the crystal size, the distribution and the concentration may be influenced. For instance, the analysis of the 14th century Islamic tin glazes from eastern Spain indicates that these samples may be produced by non-fritting methods, as the heterogeneous distribution of tin oxides may be the remains of original grains of tin oxides. In this application, additions of up to 6% are reported to be used. The cost of tin oxide rose considerably during
World War I (1914-1918), and resulted in a search for cheaper alternatives. Whilst zirconium compounds are not as effective, their low price led to a gradual increase in popularity with an associated reduction in use of tin oxide. Today, tin oxide finds limited use in glazes, generally its use is restricted to specialist low temperature applications, and by artisanal studio potters. The whiteness resulting from the use of zirconia has been described as more
clinical than that from tin oxide, and is consequently preferred in some applications. The Koninklijke Tichelaar Makkum factory, or Royal Tichelaar Makkum, based in
Makkum,
Friesland continue the production
Delftware using tin-glazed
earthenware. ==Properties==