Anticlastic curve created by raising
Raising is a metalworking technique whereby sheet metal is formed over a stake or other solid object by repeated sequences or "passes" of hammering and annealing of the metal, thereby compressing and thickening the steel into the desired shape. This technique is an essential part of metalworking; among other uses, it was used in creating medieval plate armour, and is also used to create fine silverware.
In traditional raising, sometimes referred to as Synclastic raising, the dominant curves of the object being forged are at right angles and move in the same direction; as in a bowl. This results in a surface possessing elliptic geometry.
Anticlastic raising, on the other hand, refers to shaping an object where the dominant axes move in opposite directions; a familiar example of this is a potato chip. This results in a surface possessing hyperbolic geometry.
Raising should not be confused with the other common technique for forging three-dimensional objects from two-dimensional stock, sinking/dishing where the metal is stretched to achieve the desired shape.