How did Vikings get their metals?

Recently I was able to hear Professor Joyce Hill lecture on the Vale of York Viking hoard. She holds an emeritus chair in Medieval Literature at the University of Leeds. Prof Hill is a wonderful speaker and is quite brave enough to move into archaeology or even archaeo-genetics when these disciplines appear to illuminate a point that interests her. My daughter Jess and I have seen the hoard for ourselves but the recent Viking Exhibition at the British Museum, where it was on show, was packed to bursting which made quiet contemplation impossible. I can foresee a trip to its home at the Museum of Yorkshire in the near future. I don’t have a picture of the Vale of York Hoard so the image is of another British Museum Viking silver assemblage.

Very naturally one of Prof Hill’s main enthusiasms concerns the beautiful Carolingian silver-gilt bowl into which the hoard’s ingots and silver coins were packed before burial. The bowl is a ciborium which was used to hold bread during a Christian communion service; it must have been a century old when it was used as a container. Other examples from Britain are known and one recent discovery even retains its lid. Stylistically they could all have come from the same Frankish work-shop. Given the proclivities of Vikings the Frankish silversmiths may not have been fully remunerated for their skill and trouble. In the case of Yorkshire’s Norse community the empire was about to strike back in the shape of Aethelstan, the Anglo-Saxon king of all Britain, who was shortly to make an ‘official’ visit to York. Indeed the dates of the coins suggest that the hoard’s burial was not unconnected with Aethelstan’s arrival in the new part of his kingdom.

Even when confronted with images of some rather beautiful objects I found myself wondering where all the metal had come from in the first place. Some doubtless originated in honest trading, but being paid handsomely to go away is also nice work if you can get it. The Vikings extracted vast sums in tribute from Frankia and later from Britain. We are probably talking about silver by the tonne and hundreds of kilograms of gold. Much of this will have been melted down to make the intricate jewellery items for which the Norse world is justly famous. What follows contains a good deal of speculation and I should welcome more evidence-based information from any reader. Clearly the Vikings prized the precious metals gold and silver, an enthusiasm they shared with many other societies both before and since. There is no intrinsic reason why these elements should be so highly valued, but they were. Bullion, especially silver bullion, served as the medium of exchange throughout the Norse world. As well as serving an extremely important role in Viking society silver was minted into a beautiful coinage for the contemporary English kings.

You will probably know that the metal lead, when prepared from its ore galena, contains about 2% silver. The silver was extracted by cupellation, a technique which is at least 2000 years old. Lead was heated in a flat bone ash crucible and air was blown onto the molten metal. The lead oxidised to litharge (PbO) which melted and soaked into the crucible. The bright melted silver did not oxidise and was left behind. The lead could later be recovered from the crucible. Ancient Athens was famous for its silver mines, and in Britain the Romans were extracting lead from the Mendip Hills by 50 CE. The Roman distribution of water made it necessary for them to obtain large amounts this metal. It was cast into sheets which could then be formed over a rod and soldered to make a pipe; Mendip lead has even been found in Pompeii. It seems highly likely that silver was being produced as well even at this early stage and by 70 CE Britain was the biggest supplier of lead and silver to the empire. It is known that silver was also being extracted by cupellation in Derbyshire, the evidence being some locally produced lead pigs with variable amounts of silver. I assume this process continued in the early medieval period although some Viking silver could easily be recycled Roman metal objects. The Viking silversmith’s basic raw material was often hack-silver, in other words cut up scrap.

The Vikings traded with Byzantium (Miklagard or Miklegarth) and imported Arabic silver coins from the Baghdad Caliphate, which they called Serkland. The Slavs to the east produced silver trade ingots and the spiral silver armlets known as Permian rings. This suggests they had their own sources of silver. But nothing lasts forever. The need for lead declined in the early medieval period although there was a vastly increased demand for lead flashings in the later middle ages when cathedral and castle building began. The mines from which the Arabs obtained silver were exhausted by the 10^th century, although silver mines in the German Harz mountains were being developed during this period.

Because of its chemical unreactivity the only source of gold of any importance is the native metal. It is widely distributed but the problem is to separate gold flakes from the quartz or gravels in which it occurs. In ancient times, which would include the Norse period, crushed rock was separated by water whereupon the heavy gold dust sank first in settling troughs. Later extraction with metallic mercury was practised, and finally in modern times sodium cyanide extraction. Gold is soft, being extremely malleable and ductile. It can be beaten out into thin gold leaf between vellum which could then be used for decorating leather or illuminated manuscripts. There were sources of gold in Ireland and Wales which were probably first exploited in the Bronze Age. I assume that the Romans effectively abstracted all the British gold that hadn’t been safely buried but they also had their own mines in Spain. Due to its non-reactivity gold is an easy metal to recycle. Much gold left the empire for the east in exchange for silk and other luxury goods. By the Norse period there was probably an unmet need for gold which was not fully remedied until the Spanish started to import the metal from its New World possessions nearly a millennium later.

Copper is not a precious metal but it is commonly alloyed with gold to make it harder, or with tin to produce bronze which forms the basis of much jewellery. There is evidence that copper was being extracted in Wales in the Bronze Age. Associated artefacts have been radiocarbon dated to 2000 BC. Very early BA copper seems to have come from the Wicklow Mountains in Ireland, and the Great Orme Head in North Wales is a pre-Roman (and probably a BA) copper mining site. The Romans found a significant source of copper in Cornwall but they already had abundant supplies in Cyprus and Spain. Tin is much rarer but again Cornwall was a source of this element which was subsequently traded extensively in western Europe.

Silver, gold and copper will liquefy if contained in a crucible and heated on a charcoal fire. The molten metal can then be poured into a mould and will solidify on cooling. This process is known as casting, which is also suitable for alloys with a relatively low melting point such as bronze or pewter. A ‘runner’ must be created down which the molten metal runs into the mould. One or more ‘risers’ allow gases and excess metal to escape. Excess metal forms a ‘casting jet’ which is broken off when the casting has cooled. Moulds were made of two pieces, or even three if a socketed axehead was to be produced. Moulding can be achieved with clay, or moulding sand. Highly complex shapes were produced by an alternative ‘lost wax’ (cire perdue) method. The advantage of the lost wax method is the fact that there is no ‘parting line’ or ‘flashes’ seen on the casting, which also has a very smooth surface. After casting Norse bronze brooches, manufactured in this way, could be polished and ‘fettled’, and then embellished with gold, silver and niello – a black silver sulphide paste. The results are magnificent by any artistic standards. Silver and niello brooches were very popular. In this technique a line was engraved on a silver plate with a tool that would produce undercutting. Niello was rubbed into the design and the piece reheated to make the niello molten. After sanding and polishing the niello contrasted black against a silver background.

Iron could not be treated in this way. The northern European Iron Age didn’t began until about 700 BCE. The Romans later worked iron in the Forest of Dean and the Weald of Sussex. Sweden is famous for iron ore but the Viking age smiths probably collected and dried ‘bog iron’. A simple stack of charcoal and iron ore was ignited in a tall clay container or bloomery. The temperature was increased with bellows and eventually the result were ‘blooms’ of iron. The reduction of the ore to metallic iron was a solid state process since the temperatures reached were not high enough to produce liquid iron. The blooms were subsequently re-heated and hammered to extrude the slag and consolidate the metal. Wrought iron made in this way is practically pure with about 3% residual slag. It can be worked by a blacksmith with hot hammering. Cast iron was not made in Europe until the introduction of blast furnaces in medieval times. The oldest process for making steel is cementation. In this method wrought iron bars are bedded in charcoal for seven days and heated. The bars take up carbon and and the outer parts of the bar are converted to steel. When steel is cooled slowly or annealed, it is comparatively soft. Cooled quickly in water, that is quenched, it become intensely hard and brittle. Careful reheating determines its final properties. Razors are reheated very little since they need to be very hard and undergo no shocks. Chisels must be heated to a higher temperature since although they must be as hard as possible they should not be at all brittle.

The Vikings must have understood all these processes since they required large quantities of iron for helmets, weapons, tools and agricultural implements. The English and Anglo-Scandinavian metalwork discovered during the York excavations have been studied intensively. Investigation has shown evidence of high quality steel among the edged tools. Metallurgical evidence from Hamwic, Saxon Southampton, also shows similar high quality steel in the edged tools. Examples of steel from these sites shows that there was a high and uniform carbon content. Wrought iron had a very low slag content and exceptionally high hardness values that weren’t achieved again in edged tools till after the industrial revolution. Despite this knowledge the Vikings also imported superior sword blades from the Rhineland. The Carolingian kings attempted to prevent this, an early example of arms control. Despite the manufacture of beautiful objects the Viking age was a time of considerable uncertainty:

A wayfarer should not walk unarmed,

But have his weapons to hand:

He knows not when he may need a spear,

Or what menace meet on the road.