In 1840, Mulready designed the illustrations for the postal stationery, known as Mulready stationery were introduced by the Royal Mail at the same time as the Penny Black in May 1840. They were issued in two forms; one variant was precut to a diamond or lozenge shape and folded to form an envelope that could be held together by seal at the apex of the topmost flap; and lettersheets that were cut in rectangles, folded over and sealed or tucked in.