<p>Our ancestors first learned to make iron from rocks in 1000 BC. They utilized a furnace design now called a bloomery furnace. For the next 24–26 centuries, iron was made in bloomery furnaces. There have been a few scientific studies of these furnaces and more recently many studies of ancient bloomery sites. A review of these studies is presented. It is shown that there are eight main processing variables of the bloomery process. The iron produced in the bloomery furnace is called a bloom and it is usually a low carbon iron, less than 0.1–0.2 wt.%C. Scientific studies have shown that two main variables control the average %C in the blooms, the rate of charcoal addition, and the ratio of ore to charcoal. However, there have not been studies of the distribution of carbon in the bloom and what factors control the distribution. There are two main factors involved in control of the carbon level. (1) Pure particles of iron are produced in the upper regions of the bloomery stack. As they descend the high levels of CO there causes them to increase in carbon by carburization. (2) As the particles fall past the hot blast emanating from the tuyere at the furnace bottom the carbon level will be reduced by the high CO₂ level and high temperature in this region. A bloomery experiment was conducted in which the carbon distribution in the bloom was determined. Based on the results, a hypothesis is presented for the mechanism controlling the carbon distribution.</p>