English and German pencils were not available to the French during the Napoleonic Wars ; France , under naval blockade imposed by Great Britain , was unable to import the pure graphite sticks from the British Grey Knotts mines - the only known source in the world .
France was under naval blockade imposed by Great Britain and could not import the pure graphite sticks from the British Grey Knotts mines - the only known source in the world for solid graphite .