First Fire: Most Sanitaryware is fired in a single process; so the piece is Cast, Dried, Glazed and Fired just once creating a finished piece. This can be done in a tunnel kilns or shuttle kilns but most large producers use a tunnel kiln as it is more fuel efficient.
Refire or Second Fire: After the first firing, many producers will repair any slight blemishes that are found in the glaze surface on a small number of the pieces. This involves grinding the surface and repairing it with a second glaze process before Refiring (or Second firing). This is normally done in a shuttle kilns as the numbers are smaller and variable so the shuttle kilns offers more flexibility.
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Nutec Bickley has extensive experience designing and manufacturing tunnel kilns and shuttle kilns for the sanitaryware industry.