Tin-glazing
[4] The technique originated in the Near East and reached Europe during the late Middle Ages, with a peak in Italian Renaissance maiolica.
[8][9] The earliest tin-glazed pottery appears to have been made in Abbasid Iraq (750-1258 AD)/Mesopotamia in the 8th century, fragments having been excavated during the First World War from the palace of Samarra about fifty miles north of Baghdad.
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.
[12] 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[10] From the Middle East, tin-glaze spread through the Islamic world to Spain.
In the 13th century, tin glazes reached Italy, where the earliest recorded reference to their use is in the 1330s,[13] resulting in the emergence of Italian Maiolica.
[15][16] 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.
[19] 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.
Late Italian maiolica blended oxides to produce detailed and realistic polychrome paintings, called istoriato.
[24] The disadvantage was that only a narrow group of pigments produced good colours after firing at the relatively high temperatures of up to 1000 °C.
[25] 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).
The fired vessel is dipped in a liquid glaze suspension which sticks to it, leaving a smooth and absorbent surface when dry.
The unfired glaze absorbs the pigment like fresco, making errors difficult to correct but preserving the brilliant colors of the oxides when fired.
As mentioned above, tin glaze suspension is applied to bisque or biscuit body made of calcareous clay with high content of calcium oxide.
[29] The cost of tin oxide rose considerably during World War I (1914-1918), and resulted in a search for cheaper alternatives.
[30] 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.
These factors – the high refractive index, the low solubility in glazes and the particle size make tin oxide an excellent opacifier.
This could be seen from the SEM photomicrographs of some earlier Islamic glazed ceramics, of which the particles of tin oxide are concentrated at the interface, together with the existence of wollastonite, diopside and air bubble as other opacifiers.
[31] The firing temperatures of such glazes are low, in the region of 950 – 1000 °C because of the variable degrees of solution of the individual oxides.
