From the industrial archaeology reading program. Very enlightening. I thought I knew a little about metal processing from my remediation experience, but that was confined to copper, lead, and precious metal operations; I found I was pathetically ignorant about iron and steel.

Author Robert Gordon, a Yale geophysics professor, apologizes in the front matter for excluding Mexico and including Canada in “America”. The initial source was bog iron, iron oxyhydroxide produced by bacteria; it was literally possible to grow iron ore as a crop (it took about 20 years for a bog iron deposit to renew). Using a method known for millennia, a smith threw the lump extracted from the bog on a charcoal fueled forge with a hand-pumped bellows, heated it until malleable, and hammered until the slag moved to the outside. The chemical reaction necessary was reduction – removal of oxygen – and the reducing agent was carbon monoxide; that’s still the way you make iron, although the process has become increasingly elaborate.

The next step was the blast furnace; there was one in Massachusetts by 1641. This stacked charcoal, iron ore, and limestone in a tower, set the charcoal on fire, and blew air through with water-powered bellows or piston pumps. The limestone’s there to act as a flux, combining with gangue in the ore to make an easy-to-remove calcium silicate slag; it seems that some of the early furnace operators didn’t quite understand the chemistry involved and used gabbro instead of limestone (there was just barely enough calcium in gabbro to make this work). That develops one of Gordon’s themes; until the end of the 19th century, iron working was much more of an art than a science. Iron manufacturers and iron users didn’t understand the chemistry of the smelting and refining processes or the metallurgy of the finished product but depended on years of experience and artisanal knowledge to make and use iron.

This caused some interesting problems; the US government contracted with the Franklin Institute to develop methods to test iron (Gordon claims this was the very first scientific research sponsored by the United States government). The Franklin Institute came up with a machine to pull an iron bar until it broke, thus measuring the tensile strength (there were provisions for heating or cooling the iron to test at different temperatures). However, it wasn’t understood that tensile strength is only one of the properties contributing to the overall mechanical performance of iron, especially for the applications the US government was interested in (boilers and firearms) – hardness and especially ductility were equally or more important. This lack of understanding contributed to a lot of pseudoscience about iron – that the properties were influenced by whether the iron was made with charcoal or coke or anthracite; whether the blast furnace used a hot (preheated) blast or a cold blast; how long the molten iron was held in a crucible before pouring; and so forth.

Similarly, the Americans had a very hard time with steel; early manufacturers produced steel with very irregular properties, to the extent that all major American firms using steel bought it from England (when American firms finally did get the knack of making quality steel – it turned out to hinge on properties of the clay crucibles used – they lied about the source and advertised it as “Sheffield steel”, since American steel had acquired such a bad reputation).
I learned a great deal here – the difference between a bloomery, a finery, and a puddling furnace; how a reverberatory furnace works and why you would want one; what a cementation furnace does; how blister steel becomes crucible steel; what a Bessemer converter does, and why the open-hearth furnace replaced it; and the difference between a tilt hammer, a helve hammer, and a steam hammer. There are lots of illustrations, mostly photographs of ironworks and diagrams of various kinds of equipment; maps of iron mining and iron and steel production areas; an excellent glossary; and an extensive bibliography. Gordon laments that historical museums focus on the very early sites – charcoal forges – and on large buildings – blast furnaces – but later and less spectacular developments have been ignored – there are no bloomeries, fineries, puddling furnaces, cementation furnaces, or crucible steel sites on exhibit. Very worthwhile. ( )

A good introduction to the topic.

This is an interesting book that mixes high-level overview, illustrative anecdotes, and technological detail surprisingly well. At heart this is a high-level survey of the development and decline of the North American iron industry from its Virginia origins through its eclipse by Big Steel as the twentieth century began. But there's a concurrent technical essay about the development--and shortcomings--of the mastery of various technologies over the course of the period. Both stories are told with examples from the historical record which demonstrate the analytical points the author is making. One important point Gordon makes is that the charcoal iron industry's survival into the steel era was not the result of ignorance, and that American ironworkers generally kept up to date on current technology.

The last chapter is really an appendix; it discusses the publicly-available remnants of the industry at such places as Hopewell, Pennsyvania, and Fayette, Michigan. A couple properly-labelled appendices briefly summarize metallurgical archeology and historical production levels; the second appendix is, frankly, inadequate.

The author makes it clear that knowledge of the chemistry of the processes involved in making iron was insufficiently known until the steel industry hired scientists to solve everyday problems posed by their operations. He clearly regrets that these things were not discovered earlier in the nineteenth century.

One major shortcoming, acknowledged by the author, is the lack of information about iron working in the areas settled by the Spanish. A similar summary work would certainly be useful.

I was already fairly familiar with the historical overview presented here (look at my library), but the technical discussion of metallurgical theory and practice was illuminating in ways I'd not encountered in earlier reading.

Oh, yes: Great end notes, too.

This review is also available on a dabbler's journal. ( )