How Do You Raise a Face Out of Flat Metal? Hammer It From Behind

The technique has two complementary operations that are always used together. Working from the back with rounded punches pushes the metal outward, raising the broad forms of the design into relief on the front. Working from the front with finer punches pushes metal inward, defining edges, adding texture and sharpening the detail that the first operation established. Both stretch and move the metal rather than cutting it, so nothing is lost and the sheet becomes thinner where it has been raised most. The two are alternated repeatedly, turning the work over many times as the form develops.

Supporting the sheet is the practical problem and the solution is characteristic:

• •The sheet is bedded in pitch, a thick tar-like compound in a bowl
• •Warmed pitch is soft enough to press the sheet into
• •Cooled pitch is firm enough to resist the hammer
• •It supports the sheet everywhere while allowing local movement
• •The work is warmed, lifted and rebedded to work the other side
• •The metal is annealed periodically, since hammering hardens it

Hammering deforms the crystal structure of metal and makes it progressively harder and more brittle, which is useful when strength is wanted and fatal when more shaping is required, since a work-hardened sheet cracks rather than stretching. The remedy is annealing, meaning heating the piece until the structure reorganises and the metal becomes soft again, then cooling it. A complex piece is annealed many times during its making, and forgetting to do so is the classic beginner's mistake, producing a split that cannot be repaired invisibly. Gold and silver anneal at temperatures easily reached with a hand torch, which is one reason those metals dominate the craft.

Three ways of producing a relief in metal are easily confused and the distinctions are visible on the object. Casting pours molten metal into a mould, so the piece is solid, the same thickness throughout is not required, and the back carries no trace of the front. Engraving and chasing cut or push material on one face only, so the reverse stays flat. The technique here works a sheet from both sides, so the back of the piece is a negative of the front, hollow behind every raised area, which is the clearest way to identify it. That hollowness also makes the work far lighter than a cast equivalent.

The technique is ancient and produced some of the most celebrated metalwork anywhere. Bronze Age goldwork across Europe and the Near East uses it, including the funeral masks from Mycenae. The gold objects of the Scythians and the great Iron Age cauldrons and shields of northern Europe are worked this way. Renaissance and later silversmiths used it for dishes, plaques and armour decoration. Enormous architectural applications exist, most famously the copper sheets forming the Statue of Liberty, which were hammered over wooden forms by exactly this method and are only a few millimetres thick over their whole surface.

Punching from the back raises broad forms and punching from the front sharpens them, with the sheet bedded in pitch that supports it everywhere while letting it move locally. Nothing is cut away, so the metal thins where it is raised most, and it must be annealed repeatedly or it cracks. Mycenaean gold masks, Scythian work and the copper skin of the Statue of Liberty are all made this way.