Anthracite and a good blower. Never saw "rust" that color before - might be a sulfide or something. Roy,=20 There is a yellow iron sulfide, so I guess that's possible. Doesn't = strike me as real likely though. =20 The pure iron comes with a powdery red rust, but I've only seen black = scale on it out of the forge. I haven't let a piece rust to see what that = would look like. Bruce NJ