How Were Viking Tortoiseshell Brooches Cast by Medieval Metalsmiths?

Written by Simon Williams

Walk into any major Viking Age exhibition and you will find them within the first few cases. Two large oval bronze objects, their surfaces covered in dense interlace decoration, their edges showing the slight asymmetry that distinguishes a hand-finished casting from a mechanically produced form. The labels will call them oval brooches, or tortoiseshell brooches, and they will almost always be displayed in pairs, because that is how they were worn.

These objects are the single most archaeologically reliable marker of Norse female presence at any site in the Viking world. Wherever Norse women went, from the Norwegian fjords to the Irish Sea coast, from the Danelaw settlements of Yorkshire to the Varangian trading towns of Russia, the oval brooch went with them. It fastened the straps of the Norse apron dress at both shoulders, making it simultaneously a practical garment fastener, a canvas for the highest-quality surface decoration available to the Norse smith, and a declaration of cultural identity that was legible across the entire Viking world.

Yet for all their ubiquity and their importance in the archaeological record, the production process behind the tortoiseshell brooch is remarkably little known outside specialist scholarship. How were these objects actually made? What did the production of a pair of oval brooches require in terms of skill, materials, and equipment? And what does the manufacturing evidence tell us about how the Norse metalworking tradition organised itself to produce objects in quantity without sacrificing quality?

What Is a Tortoiseshell Brooch?

The name tortoiseshell brooch comes from the domed oval form of the object, which bears a passing resemblance to the shell of a tortoise when viewed from above. It is a modern descriptive term rather than a Norse one: the Old Norse sources refer to these objects simply as brooches, and the specific term we use today developed in the 19th century archaeological literature.

The brooch consists of three main elements. The body is a large domed oval casting, typically between 9 and 13 centimetres in length, whose upper surface carries the decorative programme that makes the object visually distinctive. The back plate is a separate flat oval casting that forms the underside of the brooch and carries the pin mechanism. The pin itself is typically made from iron or bronze wire, attached to the back plate by a pin catch and hinge arrangement that allows the pin to be inserted through the fabric of the dress strap and secured.

The domed upper surface is the site of the decorative investment. The great majority of oval brooches are decorated in the Borre style interlace and gripping beast tradition, though examples in the Jelling, Mammen, and later styles are also known. The decoration is integral to the casting, meaning it was modelled in the wax or carved into the mould before casting rather than added to the surface of a finished piece, which has important implications for understanding the production process.

The typological classification of oval brooches was established by the Norwegian archaeologist Jan Petersen in his 1928 study Vikingetidens smykker, which identified a series of brooch types based on their decorative programmes and formal characteristics. Petersen's typology, designated by letters from A through to R with subdivisions, remains the standard classification system used by Viking Age archaeologists today and provides the framework within which individual brooch finds are located and compared.

The Lost-Wax Process: How It Actually Worked

The lost-wax casting method, known in Latin as cire perdue and documented across human metalworking traditions from the Bronze Age to the present, was the primary production method for Viking Age oval brooches. Understanding how it worked in the Norse context requires distinguishing between the method as applied to single unique objects and as applied to the serial production of brooch types in significant numbers.

For a unique object, the lost-wax process begins with the modelling of the desired form in wax. The wax model is then invested, meaning surrounded with a clay or ceramic slurry that is allowed to harden. The hardened clay mould is heated, which melts and burns out the wax, leaving a cavity in the shape of the original model. Molten metal is then poured into the cavity, the clay is broken away once the metal has cooled, and the resulting casting is cleaned and finished.

For serial production of a recurring brooch type, the process was modified. Rather than modelling each brooch individually in wax, the Norse smiths used a master model, carved in stone, bone, or metal, from which wax blanks could be pressed. The master model was pressed into a pad of clay or some similar material to create a one-sided impression, the wax was pressed into this impression to produce a wax blank matching the master form, and the blank was then invested and cast in the normal way.

This master model approach allowed the same decorative type to be reproduced consistently across multiple castings while still producing objects that were individually finished by hand and therefore not mechanically identical. The slight variations in surface detail visible between brooches of the same Petersen type are the fingerprints of this process: the same basic form, individually finished.

The clay double mould referred to in the At a Glance section describes a variant of this process in which the mould was constructed in two halves, allowing access to both faces of the casting for cleaning and finishing. This approach is particularly associated with the production of the domed oval brooch form, where the complex three-dimensional surface of the dome required a mould construction that could accommodate both the upper decorated face and the flat back plate.

The Bronze and Its Properties

The material of choice for oval brooches was bronze, a copper-tin alloy whose specific composition varied across the Viking Age production tradition but typically contained between 5 and 15 percent tin alongside the copper. The choice of bronze over silver or iron for this object type was deliberate and had specific practical and aesthetic reasons.

Bronze casts with greater fidelity to fine surface detail than iron, which made it the natural choice for an object whose primary visual value lay in the quality of its surface decoration. It is also harder than pure copper and more resistant to the mechanical wear that a functional dress fastener would experience in daily use. And it could be surface-treated after casting to produce a range of visual effects, from the natural golden-brown of freshly polished bronze to the darker patinated surface of aged metal, with some examples showing traces of gilding or tinning that would have given them a silver-like appearance when new.

The sources of copper and tin for Viking Age bronze production were distributed across northern Europe, with tin coming primarily from Cornwall in south-west England and copper from various central European sources. The availability of these materials through the same trading networks that moved silver, silk, and amber across the Viking world meant that bronze production was not constrained by geography in the way that gold production was, which contributed to the accessibility of bronze as the standard material for the mass-production end of Viking Age jewellery.

Surface Decoration: Reading the Brooch

The decorative programmes on Viking Age oval brooches are not random. They are systematic expressions of the stylistic conventions of their period, and reading them correctly requires understanding the specific formal vocabulary of the style in which each brooch was produced.

The great majority of surviving oval brooches are decorated in variants of the Borre style, which dominated Norse metalwork production from roughly 850 to 950 AD and is characterised by the gripping beast motif, symmetrical ring chains, and interlocking knotwork. Borre style brooches typically organise their decorative programme around a central boss or field of knotwork, with gripping beast heads arranged around the perimeter of the dome and ring chain elements filling the intermediate zones.

The relationship between the brooch surface decoration and the broader animal style tradition is covered in full in the Borre style gripping beast article in this series. What matters here is the manufacturing implication: the complexity of the Borre style surface, with its multiple interlocking elements arranged across a curved three-dimensional surface, required a level of model-making skill that was itself a significant component of the brooch-maker's craft. Carving a master model that would produce a satisfactory casting of a full Borre style decorative programme was not a trivial operation. It required both artistic skill and an understanding of how the casting process would translate the three-dimensional wax or carved model into metal.

Distribution and What It Tells Us

The distribution of Viking Age oval brooches is one of the most carefully mapped datasets in Norse archaeology, and the patterns it reveals are genuinely illuminating about how Norse female identity was expressed and maintained across the Viking diaspora.

Brooches of Scandinavian types have been found at Norse settlement sites across the entire range of Viking Age expansion. In the British Isles, oval brooches are documented from Norse burial and settlement contexts in Scotland, the Northern and Western Isles, northern England, and the Irish Sea zone. In Iceland, they appear from the earliest settlement period, brought by the first Norse settlers in the late 9th century. In the Varangian eastern settlements, Scandinavian-type oval brooches appear at Birka, Gnezdovo, and other major sites, marking the presence of Norse women in the cosmopolitan populations of these eastern trading towns.

The consistency of the oval brooch as a female dress fastener across all these geographically dispersed contexts is remarkable. It implies that the Norse apron dress and the brooch pair that fastened it were understood as a specifically Norse female dress tradition, maintained in diaspora contexts as a marker of cultural identity in the same way that other aspects of Norse material culture were maintained and expressed among communities living outside Scandinavia.

The burial and ritual article in this series covers the burial assemblage context of the oval brooch in detail, including its role as the defining element of the standard Norse female grave assemblage at Birka and other major cemetery sites.

The Pin Mechanism and Practical Function

The back plate of the oval brooch, less visually prominent than the decorated upper surface but equally important to the object's function, carries the pin mechanism that made the brooch work as a practical garment fastener.

The pin was typically made from iron or bronze wire, formed into a long straight pin with a small loop or hook at one end and a sharpened point at the other. It was attached to the back plate by a combination of a pin catch, a small projection through which the sharpened point could be inserted to secure the pin in the closed position, and a pin hinge, a tube or loop at the opposite end through which the pin's loop was threaded.

The length of the pin, typically 8 to 12 centimetres, was functional: it needed to be long enough to pass through the fabric of the dress strap with sufficient pin remaining to insert into the catch, but not so long as to be unwieldy in daily use. The sharpness of the point was maintained by the wearer rather than the smith, and the replacement of worn pins was a routine maintenance task throughout the brooch's working life.

The practical quality of the pin mechanism is a reminder that the oval brooch, for all the scholarly attention paid to its decorative surface, was first and foremost a working object. It fastened a dress. It was handled daily, closed and opened multiple times, and subjected to the mechanical wear of everyday use over what might have been decades of active service before being deposited in a grave or a hoard.

The Legacy of the Oval Brooch in Norse Studies

The oval brooch has a specific place in the history of Viking Age archaeology beyond its significance as an individual object type. It was one of the first Viking Age object categories to be systematically typologised, and Petersen's 1928 classification study was one of the foundational texts of modern Norse archaeology, establishing methodological approaches to typological analysis that influenced the study of other Viking Age material categories for decades.

The brooch is also one of the most accessible entry points into Viking Age material culture for non-specialist audiences, because its function is immediately intelligible, its decoration visually engaging, and its distribution genuinely dramatic in what it implies about the range and consistency of Norse female cultural practice across the Viking world.

For those drawn to the craftwork tradition the oval brooch represents, the how were Viking tortoiseshell brooches cast question connects directly to the broader metalworking tradition covered in the lost-wax casting article and the granulation and filigree article in this series. And if you want to carry something of the Norse ornamental tradition forward, the Viking collection at Histories and Castles includes pieces rooted in the same tradition of bold, identity-bearing Norse metalwork.

This article is part of the Viking Jewellery series.