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A fired visual effect on bare clay surfaces in fuel burning kilns (especially wood). Clay surfaces that have been flashed have been subjected to a thermal history of variations in flame, ash, kiln atmosphere and even imposed vapors (like salt and soda). The degree to which these forces have varied determines the visual variation across the surface of the ceramic. Historical ceramics often had flashing simply as a consequence of the lack of control of the process of clay preparation, forming, drying and firing. In recent years there has been a focus on the reproduction of this rustic look, various methods seek to reproduce the process, others only the final product. A popular method is the application of slips having a makeup likely to react with the atmosphere or flame in the kiln. Slips of high alumina content, for example, are likely to react with an atmosphere containing ash (since the ash can be high in silica and soda). Likewise, a slip high in fine silica and alumina is likely to react with fumes of soda. Slips containing some iron will exhibit differing coloration where differing amounts of flame has touched.

The chemical and process mechanism that produce this effect are not well known or understood by the vast majority of practitioners. The mystique of this is part of the attractiveness of the process.

Example of flashing on ware from a Manabigama wood fired kiln

Example of flashing on ware from a Manabigama wood fired kiln

From Robert Self. This firing went past cone 13. The body is Laguna Speckstone.

Example of flashing from wood firing

Example of flashing from wood firing

Made by Robert Self. This is Laguna White Stoneware body fired to cone 13 in a Manabigama wood fired kiln.

This piece is thrown from calcined kaolin

This piece is thrown from calcined kaolin

Calcined kaolin has zero plasticity. 25% bentonite had to be added to make it plastic enough to make this piece. Why bother? Because this will flash heavily in reduction firing.

Out Bound Links

  • (Glossary) Salt, soda firing

    Salt firing is a process where unglazed ware is fired to high temperatures and salt fumes are introduced into the kiln chamber (normally by a spray in the burner ports). The sodium in the salt forms a vapour cloud in the kiln. That sodium, along with the silica and alumina in the clay, combine to fo...

  • (Glossary) Wood Firing

    A firing technique used by necessity in many countries and by choice in others. In a properly designed kiln wood is capable of delivering high temperatures so it is possible to make stoneware and porcelain. The kiln chamber in a wood kiln subjects the ware to alot of ash and smoke and this profoundl...

By Tony Hansen

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