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The only pure iron to be found naturally on the surface of the earth arrives in the form of meteorites from outer space. The earth's crust initially contained no iron but over millions of years of volcanic action iron was gradually brought to the surface and deposited as iron ore (rocks which contain varying amounts of iron). For thousands of years people have attempted to extract the iron from its ore with varying degrees of success. It is now known that the Romans had the technology to mass produce pure iron which they used to make their armour. When the Roman Empire collapsed the technology was lost and it was not until the advent of the Industrial Revolution and a better understanding and control of the processes involved in smelting iron that something approaching pure iron could be produced in anything like commercial quantities. This early material was called wrought iron because it had to be worked by 'puddling' and hammering to rid it of impurities. Technically it was a very mild steel, but it had a fibrous structure caused by repeated hammering and drawing out. This structure gave it tensile strength which was desirable for civil engineering projects but it had a tendency to delaminate, expand and flake away as rust formed. Pure iron is 22% more corrosion resistant than wrought iron. Click here to see the results of an independent corrosion test carried out by Keighley Laboratories. Corrosion is a continuing problem for conservators - see Conservation. Mild steel was the obvious successor to wrought iron because it has greater strength and hardness, it is much cheaper and easier to make and with the advent of the modern steel mill a consistent and reliable product could be guaranteed. For the ornamental blacksmith wishing to forge metal by hand the advent of steel was not such good news. It takes longer to heat than iron and is harder to work. It is not surprising that many blacksmiths have equipped themselves with power hammers to help with the work. Wrought iron production ceased in this country in the 1970's and since then the only available material has been reclaimed salvage. THE RECENT HISTORY OF IRON The problems involved with creating massive amounts of charcoal for the furnaces had confined the smelting process to areas where woodlands and water power for the machinery were located together. It was not until Abraham Darby I (1677-1716) substituted coke for charcoal that production began to increase. However, the smelted pig iron was only suitable for foundry castings and not for forges to convert into wrought iron. It was Abraham Darby II (1711-63) who improved the quality of coke-smelted pig iron and made it suitable for forging into wrought iron. Wrought iron was the result of forging pig iron by continued hammering and re-heating in order to produce a material which was supple enough to be made into tools and implements. The process of manufacturing wrought iron was speeded up in 1784 by a method of rapid coke-smelting developed by Henry Cort (1740 -1800). The molten iron was stirred with rods and then passed between rollers reducing the time taken to convert one ton of pig iron from 12 hours to just 45 minutes. John Wilkinson (1728-1805) was the first businessman to exploit Abraham Darby II’s coke-smelting process on a large scale. He used Watt steam engines instead of water wheels to work the bellows of his furnaces enabling them to be moved to the coalfields. He not only built the first iron bridge for Abraham Darby III but also the first iron ship, the first iron lavatory and the first iron coffin - in which he was finally buried. Some key terms explained:-
For more information about iron visit the following web site: http://www.regia.org/ironwork.htm |
Electronic mail : mail@pureiron.com
pureiron.com is a trading name of Don Barker Ltd.
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