The Bronze Age in Europe began in 3000 B.C. and gave way to the Iron Age circa 1100 B.C. While the overlap of these ages occurred at different times in different places, Greece was true to the 1100 B.C. date as it began the transition to iron manufacturing and the replacement of bronze.
We begin our study by examining the technical details of iron making because they shed light on how iron processing developed and paved the way for the practical use of the metal. Although the first iron used by man came from meteorites, wrought iron was the first class of iron manufactured, perhaps as early as the second millennium B.C. Wrought iron proved inadequate for general use because slag embedded in the metal prevented it from being sufficiently hardened. To produce high quality iron, the blacksmiths of antiquity had to learn carburization (getting carbon into the iron), quenching, and tempering (strengthening through hammering). Their experience with bronze was no help because bronze production is very different and only requires hammering. The ancient smiths could produce fires that were hot enough, but it was not until they started using charcoal that they noticed carbon being taken into the metal. Quenching and tempering is a more complicated process because you have to know when the metal is ready to hammer and when to apply heat a second time.
Once the Greeks discovered carburization, they were able to produce thin carburized products (swords). For thicker uses (axes), they had to layer together a series of thin pieces of iron to overcome the problem of getting carbon into thick pieces of the metal.
Quenching is mentioned in the Odyssey, so much of the iron manufacturing technique had evolved by the time of Homer, but the timeline of the development of the full process remains obscure. Using iron artifacts for dating is difficult because the climate of the Greek Peninsula corrodes most examples beyond identification.
There is evidence of Minoan and Mycenaean iron working, but only at the tail end of the Mycenaean efforts do we see a link to what the Greeks would accomplish later. Examples of these early efforts are knives that have their handles attached with bronze rivets. Unfortunately, the sub-Mycenaean period yields little in the way of iron objects.
It’s is not until the beginning of the Proto-geometric Period that we begin to see significant iron in Attica. These objects date from the middle of the eleventh century.
During the early, middle, and late Geometric periods (ending in 700 B.C.) we see a combination or iron and bronze metalwork in graves. Iron dominates as the metal of weaponry. The reason for this is that iron is 12% lighter than bronze and able to hold its sharpness longer, making it the metal of choice for swords and spears.
Measuring the hardness of ancient objects tells us about the quality of the technique and the relative value of the materials. Copper has a Brinell (hardness) value of 35. Mix it with 10% tin produces a bronze alloy with a hardness of 88. Wrought iron is about 100 and modern steel is 100-150 before forging and 246 after. If you hammer the bronze alloy you can drive the hardness to 228, proving that bronze was adequate in hardness when compared to iron. Two Egyptian iron knives have been discovered, air dried and not quenched, with a hardness of 302 – a stunning example of craftsmanship.
In the end, there were two main difficulties with transitioning completely from bronze to iron in Greece. In the first place the process of making iron products continued to be very technical and the number of smiths with mastery over it were relatively small. Secondly, many items made of bronze were cast in molds – a process that could not be performed in iron until centuries later. The iron making skill varied by geography and some locations were decades behind others in developing the craft, probably due to the lack of skilled smiths.
Counteracting these problems was the availability of iron which was significant relative to the copper and tin supplies needed to manufacture bronze. Greece had to import both copper and tin from Cyprus and the Levant, while iron was available in the islands, Southern Peloponnese, Central Greece, and Macedonia. Manufacturing iron removed the dependence on materials from overseas and gave the Greeks the freedom to control their own supply of weapons and other metal objects.