Bill. The black stuff on the blade is what is known as iron scale a natural carbon layer due to heating and forging. Most often in many parts of the world this is physically removed to achieve polished bare metal. Shiny things seem to have a instinctive appeal. Personally I like the play of black iron scale against polished metal. I also like to see the hammer work. I feel that in much African work the actual hammering is done not just to form the blade but also to appear pleasing to the eye when one takes the time to look. I could be talking out of my
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I have found this from a definition site, not to say it does not contain carbon also-
Iron scale, the thin film which on the surface of wrought
iron in the process of forging. It consists essentially of
the magnetic oxide of iron, Fe3O4>.