A black mineral form of carbon, also known as graphite or plumbago, that actually contains no lead. It is used for giving a metallic black sheen to grates. Available in tubes, blacklead is flammable and should not be applied near a naked flame. Wear rubber gloves and reserve a polishing cloth especially for blackleading, as it stains easily.
Alternative
If you don't want to polish your grate regularly, paint it with heat-resistant paint.
