This is the another 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 from Harry Bain, editor for The Searcher.
It is useful to consider these two low melting point metals together as they share some properties, and were sometimes combined to form alloys. Tin is an attractive, clean metal often used where it comes into contact with food. Lead, on the other hand, is highly poisonous and ugly. Its only virtue is that, with a melting point of 327ºC, it is easily cast to form intricate shapes and, of course, that it gives a belting good signal on a metal detector! However, only when I started to research this article did I appreciate the importance of both lead and tin, and the many things for which they were used.
As we saw in another article, tin is a vital ingredient of bronze. Without it, copper is a soft, weak metal of limited use but combined with 10% tin we get bronze, an alloy on which civilisations were built. However, the story of tin doesn’t end with the Bronze Age. Bronze was still used in the Iron Age and tin continued to be important – particularly for the British Isles as between AD300 (when the Spanish mines failed) and 1300, Devon and Cornwall were Europe’s main source of tin. Forty-two tin ingots were found on the wreck of a Roman ship found at Bigbury Bay, Devon, in 1991.
Tin is not difficult to extract from its ore and it was cast into ingots for transportation. Tin has some useful features as well: molten tin has excellent “wetting” properties allowing it to be applied to iron and copper alloy objects to give an attractive “silvery” surface that resists corrosion and, importantly, doesn’t taint any food it comes into contact with. “Tin” cans – actually tin-plated steel – remain important today. A curious and useless feature of tin is its “creak”: if a bar of pure tin is bent, it will give a creaking sound.
The other great use of tin was as pewter, an alloy that with its low melting point of 170-230ºC, is easy to cast using clay, stone or even wooden moulds. Stone moulds for casting pewter plates and bowls are known from Roman Britain and medieval stone moulds for casting tokens, badges and other small objects also survive. On leaving the mould the rough castings could be finished on a lathe and component parts readily soldered together to form complex and well-finished objects.
Pewter was much used to make tableware and guild regulations show two different alloys were used in the medieval period: “fine metal” was tin with 1-3% copper, and “lay metal” was tin with lead. Fine metal was harder and more expensive than lay metal, and English pewter had a high reputation all over Europe, protected by the Pewterers’ Guild which looked out for dodgy dealing – that is, lay metal being sold as fine.
There was a theory that the use of leaded pewter caused the end of Roman Britain. In Britain the Romans made great use of pewter and, it has been suggested that, while the aristocracy ate of silver and the poor off pottery, the middle classes, who ran the whole show, used pewter which, with its high lead content, caused them neurological issues. However, so far as I’m aware, analysis of late Roman bones has revealed no concentration of lead.
Pewter also has its own “catastrophe theory”: that Napoleon’s army was destroyed by their pewter buttons. Tin turns to dust when frozen and while on campaign in Russia the soldiers allegedly suffered an unfortunate wardrobe malfunction. There is sadly no evidence for this story!
In Britain, lead ore occurs in the limestone districts of the Derbyshire Peak District, the Mendips and the borders of Northumberland and Durham. The main ore was galena (lead sulphide) which is easily recognised as it is black, shiny and very heavy. Most early lead mining was carried out by following rakes, or vertical seams of ore, down into the rock. It was only later that proper mines were introduced.
Prospecting for lead and tin was of great importance and miners were allowed to dig anywhere they liked, only avoiding churchyards, gardens, orchards and the highway. This led to conflict with landowners objecting to having their property covered by holes and spoil heaps. The miners had their own courts: the Stannary Courts and Parliament in the South West, and the Bar Moot Court in the Peak District.
Like tin, lead is easily smelted from its ore which , along with wood to act as a fuel, was simply piled into a bole. This was a shallow hollow on a hillside where the wind provided a natural draft. Around it was a low wall with a passage facing the prevailing wind. After a couple of days, the fire had died down and the lead had either run out of the bole or was left as a lump at its base. While simple, the process was inefficient and the slag was later re-smelted to extract further lead.
Being soft and malleable, lead can be beaten into complex shapes and welds made with a hot iron. It’s also very easy to cast and it is possible to melt it on a bonfire. When I was a boy we used to melt lead in the woods and cast it into any available shape, which might explain the strange lead objects constantly found by detectorists. I have seen lead that has been cast into clay pipe bowls, scallop shells or anything that can be pushed into the earth to form a mould.
Lead first appears in Britain during the Late Bronze Age when it was added to the copper/tin alloy. We don’t know why this was done but it may have been to make the more valuable metals go further. Some Bronze Age objects have been found to be of pure lead and would have been of little use.
A few pieces of lead have been found on Iron Age sites but things only really get going with the Roman Conquest. We have lead ingots with inscriptions dating them to AD49 (the Romans weren’t wasting time!), whilst the latest dated ingot , bearing the names of Antoninus and Verus, is AD163-169. Roman lead ingots usually weigh around 170lbs – someone pointed out that this this is a weight that it is possible to move but not possible to run away with so making theft difficult. Unlike the rectangular Roman lead ingots, those of the medieval and post-medieval periods are boat-shaped.
Much lead was used in building and plumbing – the Romans were famed for their sanitation and the rooves of medieval churches and better buildings were covered in sheet lead. This was cast on an open bed of sand to produce sheets about 4mm thick.
In the medieval period, lead was much used in the preparation of food and brewing, although it was well-known that the metal was poisonous. Lead was also used to make coffins, and later the gun shot used to put people in them.
The images included here give some idea of the wide range of lead objects recorded by the PAS. Unfortunately, we aren’t usually able to distinguish between lead, tin and pewter.