anti-clastic raising

Anti-clastic raising is a technique whereby sheet metal is shaped so that two dominant axes curve in opposite directions, yielding a saddle shape. It is done by hammering the metal on a sinusoidal (snake-shaped) stake, compressing the center of the sheet and stretching its edges. This forces two sides to curl under and two sides to curve upward, resulting in the classic anticlastic form, shown to the left.