Nailing down Iron Artifacts
Iron is a common material used to create tools, weapons, and everyday equipment. It is distinguishable from other metals as it is magnetic and corrodes into rust. It is a very common find for archaeologists on historic sites in Ontario as it dates back to European contact. Iron was introduced from Europe in the 15th century.
The most common iron artifacts found on historical sites are nails. Nails have changed throughout the years as different processes have become available. By looking for different features, archaeologists are able to tell how old a building might be.
Without the use of a blast furnace, it was only possible to heat iron to a point where it became soft enough to work with tools (creating wrought iron objects). These objects were filled with impurities and were generally weak in comparison to purer iron objects.
Blast furnaces work by inserting iron rocks into the top of the furnace and adding fuel for the fire (wood charcoal and other flammables). Once temperatures reach an excess of 1,538 degrees Celcius, the iron ore melts and flows to the bottom of the furnace. The impurities (slag) separate from the pure iron as they are of a lighter composition. Slag is made up of glass-like substance due to the silica within the melting rocks. Once melted, the molten iron can be extracted and poured into a mould of any shape or size, creating cast iron.
Types of Iron:
Wrought Iron is created from low carbon iron and contains a lot of silica, making it the weak. It was common in early history as it was easier to produce than cast iron. Its popularity declined as steel became more available. It is no longer produced commercially (wrought iron gates for example are now made from a mild steel).
Cast Iron is made by melting iron in a blast furnace and separating the silica from the pure iron. The iron is then poured into a mould to form an object. As a result, the process creates cast lines, a noted feature of any casting process.
Steel is simply a more carbon rich iron, making it more rigid and stronger.