Heikki Seppä (1927–2010) was a Finnish-American goldsmith and educator whose systematic approach to forming sheet metal fundamentally reshaped studio jewellery practice in the latter half of the twentieth century. Working primarily at Washington University in St Louis, where he taught for more than two decades, Seppä developed and codified a family of raising techniques — most notably anticlastic raising — that allowed metalsmiths to produce complex, doubly curved, organic forms from flat sheet without recourse to casting, fabrication, or extensive soldering. His 1978 text Form Emphasis for Metalsmiths, published by Kent State University Press, became one of the most widely assigned books in studio metalsmithing education and remains a standard reference in the field.

The Geometry of Forming: Anticlastic and Synclastic Surfaces

To understand Seppä's contribution, it is necessary to distinguish between the two fundamental categories of doubly curved surface that metalsmithing can produce.

• Synclastic surfaces curve in the same direction along both axes — a dome or a bowl is the classic example. The metal at the centre must be compressed or the edges stretched; traditional raising over a domed stake achieves this. Synclastic forms have been central to hollowware and vessel-making for millennia.
• Anticlastic surfaces curve in opposite directions along perpendicular axes, producing a saddle shape — mathematically, a surface of negative Gaussian curvature. A horse's saddle, a Pringle crisp, or the flare of a trumpet bell all approximate anticlastic geometry. Achieving this in metal requires the edges of a strip or sheet to be stretched while the centre is simultaneously compressed, or vice versa, depending on the axis of attack.

While anticlastic geometry had appeared sporadically in decorative metalwork — notably in certain Scandinavian and pre-Columbian traditions — Seppä was the first to analyse it rigorously as a teachable system and to develop the specific stakes, hammers, and hammer sequences needed to produce it reliably and repeatably.

Tools and Process

Anticlastic raising as Seppä formalised it requires a relatively modest toolkit, though the skill demanded of the practitioner is considerable. The essential elements are:

• Anticlastic stakes: narrow, convex stakes — sometimes called sinusoidal or saddle stakes — whose working surface curves along its length. The metal is draped over the stake and hammered so that the edges flare outward while the spine tightens. Seppä designed and described specific stake profiles suited to different radii of curvature.
• Raising hammers: typically narrow-faced or cross-peen hammers that concentrate force along a controlled line rather than a broad area, allowing the smith to direct compression and stretching with precision.
• Annealing: work-hardening is rapid in anticlastic raising, and frequent annealing — heating the metal to relieve stress — is essential to prevent cracking. Seppä's method is iterative: raise a little, anneal, raise further.

The starting material is most commonly fine silver, sterling silver, or fine gold, all of which have sufficient ductility to sustain the repeated deformation the technique demands. Copper and brass are widely used for practice and for finished work where cost is a consideration. The gauge of sheet varies with the intended scale of the piece, but Seppä's jewellery-scale work typically employed sheet in the range of 0.8 to 1.5 mm.

A characteristic Seppä form begins as a flat strip or disc. Through successive passes over the stake — each pass working slightly further from the previous — the metal develops its saddle curvature. The smith controls the degree of flare, the tightness of the spine, and the overall silhouette by varying hammer angle, stroke weight, and the position of the work on the stake. The result can range from a gently undulating bracelet cuff to a dramatically flared collar or a tightly coiled brooch element with almost architectural rigidity.

Seppä's Pedagogical Legacy

Seppä's influence was transmitted as much through teaching as through his published work. At Washington University he trained a generation of studio metalsmiths who went on to teach in art schools and university programmes across North America and beyond. His workshops — offered through the Society of North American Goldsmiths (SNAG) and other organisations — introduced the techniques to working jewellers who had not encountered them in formal education.

Form Emphasis for Metalsmiths is notable not only for its technical content but for its philosophical stance. Seppä argued that form itself — the three-dimensional organisation of surface — should be the primary expressive concern of the metalsmith, rather than surface decoration, stone setting, or the representation of external subjects. This position aligned him with the broader studio craft movement's insistence on the intrinsic value of material and process, and gave his technical instruction an aesthetic and intellectual framework that resonated with art-school audiences.

SNAG recognised Seppä's contributions with its Lifetime Achievement Award, and his work is held in the permanent collections of several American craft museums. His influence is visible in the curricula of virtually every serious metalsmithing programme in North America, where anticlastic and synclastic raising are now considered foundational skills alongside fabrication, casting, and forging.

Anticlastic Raising in Contemporary Practice

Since Seppä's codification of the technique, anticlastic raising has been extended and elaborated by subsequent generations of metalsmiths. Cynthia Eid, among others, has published further technical refinements and explored the combination of anticlastic raising with hydraulic die-forming and other contemporary metalsmithing methods. The technique has also been adapted for use with non-precious metals in sculptural contexts well beyond the jewellery scale.

In the jewellery trade, anticlastic-raised pieces are recognisable by their characteristic flowing, saddle-curved profiles — forms that are impossible to achieve by casting or simple bending and that carry an unmistakable quality of having been worked directly by hand. This quality, and the relative rarity of smiths trained to a high level in the technique, means that accomplished anticlastic work commands respect among collectors of studio jewellery and at craft auction.

The technique remains most strongly associated with the North American studio jewellery tradition, though it has been taught and practised in Europe and Australia. Its continued presence in art-school curricula ensures that Seppä's analytical framework — the idea that sheet metal can be systematically guided into any doubly curved surface through controlled hammering — remains alive and generative in contemporary metalsmithing.

Further Reading

• Society of North American Goldsmiths (SNAG) — snagmetalsmith.org
• Ganoksin: Anticlastic Raising resources — ganoksin.com