Glazing of ceramic articles.

Glazing is important in white wares and table wares. A glaze is a thin coating of glass that is melted to the surface of the more or less porous ceramic material. In other words glaze is applied on the surface to cover the pores which are present in all cases of ceramics, except hard porcelain. In the case of common clay products obtain at low temperature, the number of pores is large, but they are also present and n small number in white wares, obtained at comparatively higher temperature. In the case of hard porcelain, these pores are closed up as a result of vitrification to about 1400 degree celcius ( at which porcelain is produced ). A glaze is a fine powder, consisting of a mixture of glass forming materials of proper composition, e.g lead silicate, borosilicate, e.t.c. A glaze contains refractory materials, such as feldspar, silica, China clay and fluxes, such as soda, potash, fluorspar, and borax in different proportions. Different combinations of this materials and different temperature at which they are fired give a wide range of texture and quality. The glaze may be put on the wares by dipping, spraying, or brushing with great care.

The purpose of Glazing is many fold. For example

(a) To produce decorative effect

(b) To improve the appearance of articles

(c) To improve the durability of ceramics article

(d) To prevent the article from environmental and atmospheric effect

(e) To make the surface impervious to liquid