Page 40 - Curriculum Visions Dynamic Book

(Below) A Roman legionary soldier. His helmet was made from copper in early legions. But as iron became available, it was made from iron. The javelin tip is iron, the body armor is also iron, as is the sword (gladius) hanging from the belt. On the shield only the boss is iron; the
rest is wood.
free from rocks unless another substance is present. This material is called a flux. Iron oxide is a flux, and it is commonly found in rocks. As a result, by chance all of the materials needed to release metals from their rocks were present in some ancient hearths.
Iron melts at a much higher temperature (1,540°C) than copper, gold, silver, lead, or tin. As a result, iron would not have been separated from its rock in simple charcoal fires. But since iron occurred naturally in many of the rocks used to obtain copper, occasionally the temperature in the hearth rose enough for the iron to change from a solid to a spongy metal paste, something we now call a bloom. It contained impurities that we now call slag. The first use of iron therefore dates from the Bronze Age, just as the first use of bronze dates from the Stone Age.
By 1200 b.c., however, iron was being more widely used. This is the date usually considered to be when the
Bronze Age gave way to the Iron Age. Again, not all regions changed at the same time, so the Iron Age started
in some regions much earlier than others.
In the Middle East metalworkers realized that
a higher-temperature fire could be made by using bellows. They also realized that
these temperatures could be reached more easily in a special kind of oven rather than on an open hearth.
By making these two changes, fires could be made to reach temperatures of about 1,200°C.
However, the iron they made was not fully molten, but a plastic mixture of iron and slag. The iron was made more usable by reheating
and hammering it many times. During this process the slag was mostly removed. The
finished material – the result of hammering – is wrought iron.
Iron comes in two forms: wrought iron and cast iron. Cast iron was discovered much later than wrought iron. To make cast iron, the iron
has to be fully molten. Then it soaks up much more carbon from the fuel. Cast iron with about
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