Silver quarter short proof sets, reviving the tradition of 90% silver issues, had a fraction of the productions of regular proof sets. In fact, this 2006 silver quarter set's mintage of 531,000 was just over a quarter of the production of the regular proof set that year. Included are 90% silver proof tributes to Nevada, Nebraska, Colorado, North Dakota and South Dakota featuring crisp, double-struck engravings and dazzling mirror backgrounds.