Re: How did ancient metallurgists think to reduce iron oxide to iron? Doweknow?

We do not know for sure how and why particular scientific advances were achieved at particular times by the ancients. Unfortunately there is no such thing as fossilized brainwaves for archaeologists or palaeontologists to collect. But there is plenty of evidence of the activities, rather than the thinking, of the ancients. We have to make commonsense speculations about the underlying thinking.

To understand the particular issues around the entry into the iron age, it is important to know the chemistry and metallurgy, and the order in which things were achieved. There is plenty of hard evidence for the order, because the fireplaces (hearths) that ancient metallurgists used leave plenty of hard evidence, as do the metallic artefacts that they produced.

The key to the story is not iron, but copper. Copper is more easily produced than iron by carbon reduction. Moreover, when copper was first produced, the product was recognizable, because unlike iron, metallic copper is occasionally found naturally. Also copper melts at a lower temperature than iron, and can be worked by beating at much lower temperatures than iron. So discovery of most of the secrets of ironworking probably did not involve iron.

The steps then would run somewhat as follows:

1. Metallic copper discovered.
2. Discovery that metallic copper could be worked in a fire -- after all, wooden spear points are hardened by fire.
3. Discovery that blue & green rocks produced metallic copper in a fire -- the first carbon reduction, as a reaction with charcoal. Probably an accidental discovery. Rocks were often used to line or surround hearths and firepits, and may have been heated in the fire for heat storage and cooking purposes.
4. Discovery of metallic tin -- another carbon reduction, which goes nearly as easily as the reduction of copper ores. Tin ores are grey or white, and harder to recognize than copper ores. Tin can be melted in a normal fire.
5. Discovery that forced air can make fires hotter, and metals easier to work. It is possible that temperatures hot enough to make molten copper were produced at this stage. Copper objects which are cast rather than beaten start to appear.
6. Alloying of copper and tin to make bronze -- the first metal that was hard enough to compete with stone for weapons and tools; copper, tin, and lead are all soft metals.
7. Discovery that a new metal could be produced by forced air carbon reduction of red rocks -- the first iron.
8. (much later) Discovery that a very useful and hard metal could be made from the iron by burning out some of the excess carbon at high temperature. It should be stressed that early iron would not have been as hard and useful a material as bronze.