Ceramics - How it's made | Ceramic Tiles

 

GLAZING 

We have now to return to our glazed tile manufacture and deal with the second main stage of the process – that of glazing. 

While the departments described have brought the tiles destined for glazing as far as the biscuit state, another section of the Works has been engaged in preparing the glaze with which they are to be coated. 

Fritting. Molten glass running off from the kiln

This glaze is simply a form of glass, so that one part of the tile-making process is carried out in what is in effect a miniature glass factory. Here such materials as felspar, China clay, flint, soda, potash, lime, and oxide of lead are mixed together in carefully determined proportions, placed in a special form of kiln, and fired to a white heat. The molten glass thus formed is run off into water, by which means it is suddenly and violently chilled. The effect of this is that it sets in bent and shattered pieces, with the result that the " frit "– as this glassy material is called  - is much more amenable to the next treatment it is to receive – that of grinding – than if it had been allowed to cool gradually. The grinding is done in rubber-lined cylinders; and as plenty of water is introduced with the frit, the product of the process is a "slop" or thick liquid. There are of course many types of glaze – some will fire clear, some opaque, some bright, some matt – but all are based on a frit such as that described. The different colours are obtained by adding to the "slop" glaze certain staining materials, notably certain metallic oxides such as those of copper, manganese, iron, cobalt, and uranium. The purpose of the glaze in tile manufacture is both utilitarian and aesthetic: utilitarian in that it seals the pores of the biscuit, thus providing an article that does not harbour dirt and is therefore hygienic; aesthetic in that it endows the tile with a pleasing 
– often a very beautiful – finish such as it does not possess in the biscuit state. 

A corner of the colour-glaze room.
Tubs of glaze ready for use.

 

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From: "A Century of Progress 1837-1937" a publication to commemorate The Centenary of Richards Tiles Ltd.