The fronts of two cards and the back of another (the only one having this “chop” from the Opium War Museum in Dongguan), representing ten cards issued by China Post with pre-printed postage.  We’re not certain how many opium postcards there are in the world — probably a few from Southeast Asia and the like — but here’s a start for you.  The front of the set’s cardboard cover only is smudged with some ink transfer from those chops.  It does not affect the postcards.  Grade: 1