A slight, but possibly related, thread drift..

Last night we watched an episode of RICKY & RALF'S VERY NORTHERN ROAD TRIP
on UK Gold catch up..

[The Cumbria and Lake district episode]

The segment exploring the Pencil Museum, explained the origins of the term "Black Market",
in relation to the discovery and exploitation of the local raw resource Graphite;
and it's properties as a darkening colourant for white skin...