Fig. 41. Prehistoric domed tombs built on the principle of corbelling (§ [116]): a probable example of the spread of a culture device over a continent. Above, Mycenæ, Greece; middle, Alcalar, Portugal; below, New Grange, Ireland. The Mycenæan structure, 1500 B.C. or after, at the verge of the Iron Age, is probably later by some 1,000 years than the others, which are late Neolithic with copper first appearing; and its workmanship is far superior. (After Sophus Müller and Déchelette.)
227. Iron
Iron was worked by man about two thousand years later than bronze. It is a far more abundant metal than copper, and though it melts at a higher temperature, is not naturally harder to extract from some of its ores. The reason for its lateness of use is not wholly explained. It is likely that the first use of metals was of those, like gold and copper, that are found in the pure metallic state and, being rather soft, could be treated by hammering without heat—by processes more or less familiar to stone age culture. It is known that fair amounts of copper were worked in this way by many tribes of North American Indians, who got their supplies from the Lake Superior deposits and the Copper River placers in Alaska. If the same thing happened in the most progressive parts of the Eastern Hemisphere some 6,000 years ago, acquaintance with the metal may before long have been succeeded by the invention of the arts of casting and extracting it from its ores. When, not many centuries later, the hardening powers of an admixture of tin were discovered and bronze with its far greater serviceability for tools became known, a powerful impetus was surely given to the new metallurgy, which was restricted only by the limitations of the supply of metal, especially tin. Progress went on in the direction first taken; the alloy became better balanced, molds and casting processes superior, the forms attempted more adventurous or efficient. For many centuries iron ores were disregarded; the bronze habit intensified. Finally, accident may have brought the discovery of iron; or shortage of bronze led to experimenting with other ores; and a new age dawned.
Whatever the forces at work, the actual events were clearly those outlined. And it is interesting that the New World furnishes an exact parallel with its three areas and stages of native copper, smelted copper and gold, and bronze (§ [108], [196]), and with only the final period of iron unattained at the time of discovery.
228. First Use and Spread of Iron
Some of the earliest known cases of the use of iron were decorative: for jewelry, or as inlay upon bronze. Finds of this sort have been made in Switzerland, Germany, Greece, and the Caucasus. Once however the extraction of the new material had become known, its abundance was so great as to further its employment, which grew fairly rapidly, though held back by several factors. One of these retarding causes was the prevalence of the casting process, which had become definitely established for bronze and was carried on with great skill, whereas iron lends itself to ready casting only in a foundry and for objects of larger size than were in customary use among the ancients. They forged their iron, and this new art had to be gradually learned. At its best, it could not produce some of the finer results of casting; in ornaments and statuettes, for instance.
Wrought iron is comparatively soft. A bronze knife will cut or shave better than a forged iron one. It was not until it was discovered that the iron from certain ores could be converted into steel by tempering—plunging the heated implement into water—that the new metal became a tool material superior to bronze. The invention of tempering seems to have followed fairly soon after the discovery of iron. But some centuries elapsed before this art became at all general.