FF DIN in use for a set of Swiss stamps commemorating the inauguration of the Gotthard Base Tunnel on 1 June 2016. The world’s longest railway and deepest traffic tunnel connects Erstfeld in the canton of Uri and Bodio in Ticino.
The triptych featuring two stamps and a connecting pictorial bridge was designed by Vaudeville Studios in Zürich. The red part includes real Gotthard gneiss. From NZZ (translated):
Of the 28 million tons of material that was broken out of the mountain, around 15 kilograms of rock went to the post office. This was processed into a fine powder and then applied to the stamps using a special varnish in a custom printing process.