Forge welding is a solid-state joining technique in which two pieces of metal are heated to plastic temperature, brought into intimate contact, and joined under mechanical pressure. The technique predates fusion welding and gas welding by millennia and remains in use in studio jewellery practice, particularly for laminated and pattern-welded constructions.

Process

In forge welding, the pieces to be joined are cleaned of oxide and brought to a temperature at which the metal is sufficiently soft to deform under hammer or press without melting. For mild steel, this is approximately 1,200 to 1,300 degrees Celsius, slightly below the melting point of approximately 1,500 degrees. For wrought iron, the welding range is similar. For pure iron, the range is narrower and more demanding. The cleaned, heated surfaces are pressed together, and a flux (typically borax or a borax-and-iron-oxide mixture) is used to displace residual oxide and to ensure intimate metal-to-metal contact.

The bond is achieved through diffusion of metal atoms across the interface and the mechanical interlocking of the two surfaces under deformation. The result, when properly executed, is a joint indistinguishable in cross-section from the parent metal. When improperly executed, the joint may show a cold-shut line, a visible interface, or actual delamination under stress.

Application in jewellery

The principal application of forge welding in contemporary jewellery practice is the production of mokume gane, the Japanese laminated metal technique in which sheets of contrasting metals (gold, silver, copper, shibuichi, shakudo) are forge-welded into a single laminated billet. The billet is then carved, rolled, twisted, or otherwise manipulated to expose the layered structure as a decorative pattern. The technique was developed in seventeenth-century Japan for sword fittings and was adapted for jewellery use principally in the late twentieth century by makers including Hiroko Sato Pijanowski, Steve Midgett, and James Binnion.

Forge welding is also used in pattern-welded steel for jewellery applications, including titanium and damascus-pattern wedding rings. The damascus-pattern jewellery industry, which grew significantly in the 2000s and 2010s, relies on forge-welded billets of contrasting steels (typically high-carbon and nickel-bearing low-carbon steels) that are then etched in dilute acid to reveal the layered pattern.

The technique is distinct from fusion welding, in which the metal at the joint is melted; from soldering, in which a lower-melting alloy fills the joint; and from braising, which uses a brass alloy as filler. Forge welding requires no filler material, and the temperature remains below the melting point of the parent metal throughout. The mechanical strength of a properly executed forge weld is comparable to the parent metal.

Tools and skill

Forge welding requires a coal, gas, or induction forge capable of reaching welding temperature; a clean anvil; appropriate tongs; a hammer or hydraulic press; and judgement of metal temperature by colour and feel. The traditional craft skill is the recognition of welding heat by the colour of the metal — typically a yellow-white that the smith learns to identify by eye in shop lighting. Modern practice may also use thermocouples or pyrometers, particularly in production of mokume gane where the welding temperature for noble metal laminates is more critical and the welding window narrower than for mild steel.

Studio jewellers producing forge-welded work typically dedicate equipment to the technique because of the high temperatures and the contamination risks. The technique is taught in the metalworking programmes of several professional jewellery schools, including the Penland School of Crafts, the Haystack Mountain School of Crafts, and the Revere Academy of Jewelry Arts.

Position in contemporary practice

Forge welding is a minority technique in jewellery production, in the sense that it is not used for ordinary chain, settings, or shanks. Where it is used — in mokume gane, in damascus jewellery, and in certain art-jewellery laminate constructions — it remains the only method that produces the visual character of true layered metal. The principal alternatives, including diffusion bonding and electron-beam welding, have been used in industrial production but do not produce the visual outcomes that are the point of laminated jewellery work. The technique is durable, and forge-welded billets prepared with appropriate care show no separation under normal wear conditions.