Page 38 - Curriculum Visions Dynamic Book

into moulds to make shapes such as bowls (it is easy to cast). It also stands up well to the weather (it is slow to corrode).
Knowledge of bronze spread gradually to western Asia and then to Europe as traders took finished bronze to trade for other goods.
Once the
properties of bronze
had been discovered, people then sought
rocks with copper
and tin in them. The
tin ore cassiterite is,
for example, quite easy
to recognise from other pebbles in a river because the pebbles are very heavy for their size.
The Iron Age
There was a long gap in history
between the use of soft metals and the
later development of harder metals such as
iron. Most metals occur in rocks combined with oxygen. They are called oxides. Others combine with sulphur to form sulphides. As compounds, the metals often have a dull colour and do not look much like the pure element. When they were heated, metals did not flow from these rocks.
However, the early fires contained burned wood – charcoal. Charcoal is mostly carbon. The carbon combined with the oxygen in the rock, and it is this chemical reaction that released the metal and allowed it to run free. We now call this process smelting, and it is still the basis for releasing metals from rocks.
In practice metals still do not normally run
(Above) Roman times began in the Bronze Age, and the empire collapsed in the Iron Age. This is a bronze Roman coin showing the Emperor Hadrian. It was minted some time between
a.d. 126 and 138. Despite having been buried in soil since that time, the coin still shows a lot of detail from the original striking. This demonstrates the resistance of bronze to corrosion.
38