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Metals from the bronze age

Bronze


Bronze rapier, sword, chisel and axe

The bronze age wouldn't be the bronze age if it wasn't for the the presence of bronze. But what is bronze exactly and where does it come from? Bronze is a copper alloy. The most well known bronze used in the bronze age contains of on average 90% copper and 10% tin, but the tin content can vary from just a few percent up to 20% in the extreme cases. The addition of tin gives several advantages over using pure copper. Pure copper is very soft, and in cast state unsuitable for use in tools that require a sharp edge. It can be hardened by forging, but that still doesn't result in a very good material for tooling. The cutting edge of a soft material can't be made very sharp and it won't last long before it needs to be resharpened. People discovered that by adding another metal like tin, the material becomes much harder in cast state, and after some forging it will result in a hard and very durable material. For most tools 10% tin gives the best quality, which makes it hard, but not too brittle. Another advantage is that the addition of tin will make the metal take up less gasses when in liquid state. This makes the casting much easier, as there is less chance of bells of gass ruining the cast when the metal solidifies. The addition of tin also brings down the melting temperature from 1083ºC to around 950ºC (depending on the amount of tin), making it a bit easier to reach the melting temperature. Finally, it gives the metal a very nice looking golden color, which the bronze age people must have appreciated very much judging from the many ornaments that have been found.

Tin isn't the only metal used to alloy copper with in the bronze age. In the transition from the neolithic to the early bronze age, arsenic and antimony were also used. Arsenic was the very first material added to copper to improve its quality. It gave an alloy almost as good as pure-tin bronze. But arsenic is highly toxic, which was probably one of the reasons why other materials replaced it. In the early bronze age, both tin-bronze and the so-called "Singen-metal" were used. Singen metal contains various amounts of arsenic, antimony, nickel and tin. Tin-bronze objects in the early bronze age were mostly imported from the UK and Ireland, where tin was discovered relatively early. Objects made from Singen metal came from areas as Germany, where tin was more difficult to come by. During the middle bronze age tin-bronze was most commonly used. By the end of the bronze age, lead was added to the tin-bronze. This actually decreases the hardness of the bronze, but it makes the bronze flow better in liquid state.

Brass, which is a copper-zinc alloy, is often confused for being bronze. The two alloys can be kept apart by the color: brass is a more greenish yellow, and bronze a more reddish yellow. Zinc wasn't until after the bronze age.


Copper

Copper
Malachite
Zaire
Malachite,
Shropshite, UK
Azurite and Malachite
Shropshire, UK
Azurite and Malachite
Greece
Cuprite, with
malachite and copper
Leicestershire, UK
Chrysocolla
Chile
Chalcopyrite
Cornwall/Mid Wales,
UK
 Chalcocite
Czechoslovakia
 Chalcocite
Cornwall, UK

Copper, the main element in bronze is found in nature in various forms, as pure metal (called native copper) and as ores. These ores did not occur in the Netherlands, so all our bronze was imported from other areas, as England, Ireland, France, Germany, Denmark etc. Native copper is rare, but is sometimes found together with ores. This is probably the reason why prehistoric people learned that those ores could also be converted into copper. The three main groups of copper ores are the oxidized and sulphide ores. Oxidized ores Malachite (green in color), Azurite (blue) and Cuprite (purple) are the easiest to convert into copper. This is done by powdering the ore, and placing it in an oxygen starved charcoal fire, basically the same conditions used for melting bronze, in which the ore converts into kopper.

Above are some examples of copper ores, most of which also used in the bronze age. Considering how many different forms there are, of which some hardly conspicuous, it's amazing that people in the bronze age managed to recognize them!

For further information:
Copper minerals
Native copper examples
Bronze age mining at Mynydd Parys
 


Tin

Tin
Cassiterite 
(tinstone pebble)
Cornwall, UK
 Cassiterite (mined)
Cornwall, UK

Tin ore occurs in very few places, and is found as only one type of ore: Cassiterite, a tin-oxide. Tin was found in Cornwall, in Ireland (small amounts), one location in France and two locations in Germany. In Cornwall, the ore was mostly found as dark colored pebbles, which were found in the glacial deposites. The same ore also occures deeper in the ground, where it was mined in more recent times. Below are examples of the ore in pebble from, and in freshly mined form.

The smelting of tin ore in to tin is basically the same as for copper-oxides, though it takes one extra step. As the type of rock in which the ore occurs inhibits the smelting, the ore first has to be seperated from the rock.
 


Lead

Lead
Galena

In the late bronze age, lead was being added to bronze. This did nothing to enhance the quality of bronze objects, it actually brought down the hardness of the metal. The advantage of adding lead is in the difference it makes during casting. Lead enhances the liquidity of molten bronze, and this enables finer and more complex castings. In the UK and France several lead chisels and socketed axes have been found, which are interpreted as intended for investment casting (or lost-lead casting). First a lead version would haven been cast in a bronze or stone mould, which was then it was wrapped in clay, the lead molten out, leaving a mould ready for casting a bronze axe or chisel. Lead was found as galena, a lead-sulfide.
 


Antimony

Antimony

Antimony is one of the metals that was used alongside arsenic and tin (so-called "Singen metal") in the early bronzes. It was no longer used when tin became the primary alloying material for bronze. Antimony can be found in as native metal (very rare) and as the ores Stibnite and Jamesonite.
 


Arsenic

Arsenic is highly toxic, hence why I don't have an example to show here. Arsenic was the first metal that was purposely used to alloy copper with. Only a few percents are needed to give the copper a hardness that's comparible with an average tin-bronze. Some copper ores naturally contain arsenic. The coppersmiths would have noticed the difference in quality of the copper from these sites, and eventually would have discovered that it's the presence of arsenic enhancing the properties of the copper taken from these ores. From then on arsenic was added on purpose, either as metal, or as ore straight into the molten copper. The toxicity of arsenic wouldn't have done the copper smiths any good (although a certain amount immunity can be build up), so this might be a reason why it was later replaced by tin (along with the color of tin-bronze).
 


Gold

Gold bracelet
Gold in quartz,
Russia

Aside from bronze, gold was also used in the bronze age, in the form of ornaments. Only a handfull of gold items was found in this region, a few bracelets and some spirals of gold wire. Gold occurs only in native form, so it can be used directly. It occurs in quartz deposites, or washed out as loose pebbles or grains in river beds. Native gold often contains varying amounts of silver, which could not be separated in the bronze age. When the content of silver was high, and therefore the gold less yellow in color, copper was sometimes added to make the metal more yellow in color. Therefore prehistoric gold sometimes contains only a relatively small amount of actual gold, and have a varying intensity in color.
 

Iron

Iron? In the bronze age? Yep, the Netherlands has one of the oldest known examples of iron made by man. In Bargeroosterveld a foothpath made from wooden planks has been found, which lead into the hard of a bog to a location rich in iron ore. On this path, which dates to around 1500BC, a 4cm long iron pin was found. Nearby, in Emmen, a bronze age village was found, where slag has been discovered resulting from iron smelting. This however did not lead to the start of an iron age, possibly because the method of iron making wasn't suitable for making larger tools. The iron age didn't start until 800BC, when the art of iron smelting and forging was introduced, possibly for the second time.