Do not use a common wire brush from the hardware store. Those brushes are not safe for food, grills or pots. Common steel wire brushes do leave a dark residue, and that may be what you keep seeing as dark smudge upon cleaning your cast iron.
Get a wire brush from a restaurant supply house or get a quality brand BBQ grill brush from a department store or cooking section of the hardware store.
Better yet, do not use a grill brush on your cast iron. Follow cleaning guidelines in this article.
Do not use a common wire brush from the hardware store. Those brushes are not safe for food, grills or pots. Common steel wire brushes do leave a dark residue, and that may be what you keep seeing as dark smudge upon cleaning your cast iron.
Get a wire brush from a restaurant supply house or get a quality brand BBQ grill brush from a department store or cooking section of the hardware store.
Better yet, do not use a grill brush on your cast iron. Follow cleaning guidelines in this article.