This is the next in our series of posts on metal-working written by Dr. Kevin Leahy, PAS National Finds Adviser. The articles were first published in The Searcher magazine and are reproduced here with kind permission of Harry Bain, editor for The Searcher.
The arrival of the Romans brought many changes to Britain – towns, villas, plumbing and a sudden abundance of small metal objects. While Roman gold is relatively uncommon, we have some amazing hoards: the Thetford Treasure, found in 1979, contained 22 gold finger rings, four bracelets and five necklaces. Even more startling was the Hoxne hoard from Suffolk, found in 1992, with six gold necklaces, three rings and 19 bracelets, along with 565 gold coins, 14,191 silver coins and 24 bronze coins, the latest of which dated to AD408. The workmanship of the gold was typically late Roman – filigree rings with settings for glass or semi-precious gems (removed before burial) and sheet gold bracelets (actually closed bangles), some bearing repoussé decoration resembling basket weave, others are “opus interrasile” where the gold is perforated giving a lace-like effect.
Was any of this stuff made in Britain? There is evidence for a goldsmith working at Malton in North Yorkshire where an inscription was found reading “FELICITER SIT GENIO LOCI SERVVLE VTERE FELIX TABERNAM AVREFICINAM” (Good luck the Genius (spirit) of this place. Young slave, use to your good fortune this goldsmith’s shop).
The PAS recorded 204 pieces of Roman gold plus 148 gold coins, finger rings being themost common item of Roman gold jewellery with 121 finds. By the Roman period metallurgical techniques had developed allowing improved control over the alloys used and gold objects were often made from good, pure metal. Cupellation was used to rid gold of base metal impurities by oxidation, and liquidation and amalgamation using mercury came into use.
The PAS has recorded a total of 473 items of Anglo-Saxon gold, including 119 gold coins. The amazing Staffordshire Hoard has not been included here as it is a one-off that distorts the overall picture. If we look more closely at Anglo-Saxon gold use, an interesting story emerges. There doesn’t appear to have been much gold around in the 5th century (or they weren’t putting it where we can find it). From the 5th to the 6th century we have 37 records of gold objects (plus 11 coins). The most common type of object are thin bracteates with 19 finds. Silver-gilt was used in the 6th century – perhaps they aspired to gold but couldn’t get it.
Finds of early 7th century gold are more common and the PAS has recorded 136 finds (plus 61 coins), pendants being the common type of object with 62 finds. Unfortunately, (for both the Anglo-Saxons and us) things went wrong around the middle of the 7th century. The gold they used was probably coming into the country in the form of Merovingian coins which they melted down. Around AD640 the gold content of these coins plummeted, the gold being replaced by silver. By 675 the gold coinage was replaced by silver; they couldn’t get any more gold. Not only gold disappeared – garnets were no longer used and elephant ivory was no longer available. For the 366 years of the Middle and Later Anglo-Saxon period we have only 81 records (plus four coins). Finger rings are the most common object with 28 finds and there are 16 ingot fragments.
The PAS has 781 records of Medieval gold (1066-1485) including 435 coins. Rings are the most common object with 271 finds. We have 1104 records of Post-medieval gold (1486-1800) which includes 277 coins and 720 finger rings. The increasing availability of gold may reflect the massive influx from the New World mines.
Gold was always scarce and valuable, and great economy was exercised in the way that it was used. It was rarely cast; most gold objects have a hollow, box-like construction. I remember many years ago seeing a massive Roman gold ring set with an intaglio which had fallen out to reveal that the ring was hollow and quite thin – most disappointing. The economical use of gold is aided by its remarkable workability. It can be beaten to any shape, joints are easily made and, uniquely, it is possible to cold-weld it.
Gold is perfect for plating other materials. Gilding using mercury is one method but gold can also be beaten to form gold leaf, four to five millionths of an inch thick. Leaf can be used to cover other metals and materials, leaving them looking like solid gold. Gold leaf can be applied to wood and plaster and it was used to great effect on illuminated manuscripts like the 8th century “Codex Aureus” (golden book) now in Stockholm.
Filigree and granulation were much used in the decoration of gold objects. Filigree consists of gold wire, sometimes as thin as 02.mm in diameter fused to the surface of the gold. Granulation involves the attachment of small pellets of gold. We are not sure how the Anglo-Saxons made gold wire. There isn’t any evidence for the use of draw-plates of the sort used now. This leaves two possible methods: strip-twisting and block-twisting. In strip-twisting a narrow strip is cut from the edge of a thin sheet of metal. This is then twisted to form a helical tube with an open centre (like a paper straw) which is then rolled between two smooth blocks of stone to compress the tube, cold-welding it to form a round-sectioned wire. In block-twisting, a square or rectangular sectioned strip of metal is cut from the edge of a thicker sheet and then twisted so that its four edges tightly encircle it. This can then be rolled between two blocks smooth the surface and produce round wire.
While we can see how plain wire was made, we’ve not been able to discover how beaded wire was produced. Every attempt results in beads with a groove around their middle – they didn’t have this problem in the past, what did they know that we don’t? The tiny gold beads used for granulation were less of a problem. Small pieces of cut gold wire were heated on a flat surface and naturally formed balls. Strips of gold leaf were wrapped around silk to form gold thread, traces of which have been found in graves.
Once they had got their wire (beaded or unbeaded) it had to be attached to the surface of the gold. This was done by a process known as eutectic soldering. The gold wire or granules were stuck to the surface using an adhesive made up of resin mixed with a copper salt and possibly a flux. When everything is stuck in place the object is heated in a furnace. With rising temperature the organic component of the adhesive carbonises to form carbon monoxide which reduces the copper salt to copper. This is absorbed by the gold or silver to form an alloy with a lower melting point than the components (a eutectic) and this new molten alloy is carried into the joint by capillary action, pulling the components together to form a strong, tight joint. While the process is apparently simple, it was not easy to carry out as the melting point of the eutectic was not much less than that of the work piece!
Analysis of Anglo-Saxon gold shows that they were using surface enrichment to make alloys look like pure gold. This was done by leaching out the silver from the surface of the gold. We don’t know how they managed to do this but they may have surrounded the object with salt and heated it. The ingenuity of people in the past never fails to impress me. The question “how did they do that?” constantly springs to mind. The trick that really amazes me is the separation of gold from silver. Imagine you have an alloy of gold and silver and want to separate them – how would you even start? The process is actually simple: the alloy was beaten into thin sheets which were laid in a pottery container interleaved with common salt and finely crushed tile. This was then sealed and heated in a furnace to a temperature below the melting point of the alloy and held at that temperature “a day and a night”. The salt reacts with the silver in the alloy to form silver chloride which is absorbed by the tile fragments and the clay vessel. The gold remains unchanged. Once the process is complete, the silver was extracted from the silver chloride. Easy – but how did anyone ever discover this trick?