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). Historical ceramics often had flashing simply as a consequence of material quality and the nature of the fuels used in firing. In recent years there has been a focus on the reproduction of the look, various methods seek to reproduce the process, others only the final product. But the modern kilns and materials used by most are highly consistent in comparison so there is a need to understand the chemistry and process mechanisms that produce the effects to better reproduce them. Notwithstanding that, most practitioners just employ recipes they have found or received and fire as instructed. The degree to which flashing appears in the ware is attributed to the mystique of the process.
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
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
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.
Soda fired porcelain vessel by Heather Lepp
This is a small cup-sized object made from Plainsman P600 (simply composed of Tile #6 kaolin, nepheline syenite and quartz). It is valued as a product-of-the-process piece, consigned to the "kiln God" as unglazed. It exhibits carbon-trap, soda glaze deposition and flashing. The soda-vapour atmosphere of the kiln glazed one side of the vessel early enough in the firing to trap carbon under a crystal-clear glass. Often such glazes are crazed, but this one likely is not because the body contains 25% quartz, giving it a high thermal expansion. The other side of the piece exhibits tones of red, brown and yellow on the bare, vitreous porcelain surface - this is characteristic of "flashing".
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