sorry, is that from the mouth, or the pipe stem? New to me was the fact that some moths back there was an item in an antiques programme where some late C19 jewellery (necklace type pieces) were shown, and these were made of Vulcanite. You'd imagine that wearing such things in daylight would lead to much oxidation, but they looked nice and black - perhaps never worn. In the U.K. (possibly elsewhere too), in the second half of the Victorian period, and due mostly to the death of Prince Albert (Victoria's husband), it became fashionable to follow the monarch's lead and wear black as sign of mourning - often in the form of jewellery. I think mostly those pieces were made from jet, but obviously BHR also got a look in.
Actually, Dunhill calls it mouthpiece polish
And as RayMan said, I have also tried it on my Dunhill pipes, and it does not work.