Stainless steel surfaces sometimes have quite a bit of black material lodged in their tiny crevices. I don't know what it is - maybe residue of the binder used in the first printing stage? I'm pretty sure it is neither steel nor bronze. The amount of offending material varies from print to print. It is especially annoying on flat surfaces. Buffing, wire brushing and steel wool brushing do not seem to have much effect. I had some success scrubbing and washing it away with Boraxo. That was only partially effective. Does anybody know what this material is? Is there a solvent for it, or any reliable method of removing it?