Shrinking — Forging Sheet Metal Inward at the Bench
Shrinking — Forging Sheet Metal Inward at the Bench
The forging operation that compresses and thickens sheet, opposite of stretching
Shrinking is a forging operation in which sheet metal is forced to compress along its length, gathering material and thickening the section. It is the opposite of stretching, where the metal is forced to thin and lengthen. In jewellery and hollowware practice, shrinking is the technique that allows a flat or curved sheet to be drawn in to fit a smaller curve, to deepen a vessel, or to reduce a flared rim — operations that without shrinking would require cutting and rejoining the metal.
The mechanics
When a hammer strikes a sheet held at an angle against a hollow stake or shrinking block, the blow forces the metal inward at the contact point and the surrounding sheet must accommodate the deformation. If the sheet is unsupported on one side and clamped or held on the other, it will tend to gather, producing a small fold or pucker that the next hammer blow planishes back into the body of the sheet — the metal having now been redistributed inward. Repeated controlled blows propagate this gathering around a circumference and produce a measurable reduction in diameter and increase in thickness.
The operation is the basis of raising — the forging technique by which a flat disc of metal is gradually formed into a deep vessel — and of any rim-finishing where the rim must be drawn in tighter than the body. Spoons, bowls, beakers, and the deeper hollow shapes of jewellery are built principally by shrinking from sheet rather than by sinking into a depression, although the two techniques are routinely combined.
Tools
The shrinking operation requires a hollow stake or T-stake of the appropriate curvature, a raising hammer with a slightly domed face, and an annealing setup. The stake provides the anvil surface against which the metal gathers; the hammer must be heavy enough to deform the work in controlled blows but not so heavy that it tears the metal. Annealing between courses of forging is essential — sheet metal work-hardens rapidly during shrinking and will crack if forged cold beyond its limit. Silver and gold are annealed to a dull red heat and quenched; copper similarly. Steel work-hardens differently and is not normally subject to this technique in jewellery.
In bench practice
Shrinking is the more difficult half of the raising and stretching pair. The technique requires a feel for how much the metal has gathered before each blow and how to direct the hammer to redistribute the gather without buckling the sheet. Apprentices typically learn shrinking on copper before progressing to silver, both because copper is cheaper and because its slightly different work-hardening characteristics make small errors less catastrophic. The control developed in shrinking transfers directly to fine raising work and to repair operations on hollow ware where dents must be drawn out without splitting the sheet.