Ceramics - How it's made | Ceramic Tiles

 

SORTING AND SIZING 

 

unloading glost ware

Glost firing over, the tiles are taken off the trucks and sorted into their different categories according to colour, size, shape, etc., the process being greatly facilitated by the use of over-head conveyors and roller sorting tables. This done, the different groups are very carefully looked through, and any tiles that fall short of the high standard of quality we set ourselves to maintain are put aside, and either broken up, classed as "seconds," or – in the case of certain types of fault – sent back for retouching with glaze and for refiring. 

 

In the glost warehouse
sorting and inspecting coloured tiles

 

A final process in the case of white glazed tiles is that of exact size-grading, or "sizing." All earthenware contracts in the course of firing – of biscuit firing, that is, the slightly lower glost kiln temperature causing little or no further change of size. The degree of contraction varies with the degree of firing, and since it is impossible to give every tile precisely the same firing treatment (different parts of the cross-section of even the same truck-load experience slightly different temperatures) some of them contract slightly more than others. Since any notable size variation would cause trouble when the tiles came to be fixed, we make use of ingenious machines which sort them into classes with a maximum variation of a thirty-second of an inch. Great care is taken that deliveries to a given regular client, or for a given contract, are as far as possible of the same exact size, our large output placing us in a very favourable position in this respect. Particulars of the precise size of the units they contain are printed or stencilled on all packages of white glazed tiles, and tile fixing firms, by paying attention to these, may easily avoid the difficulties arising from size variation. Coloured tiles 
are sized in the biscuit state, different exact sizes being allotted to different colours. 

 

size-grading white-glazed tiles

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