The total numbered issued up to Dec. 31, 1869 was 18,358, when it became obsolete. Evidence points to there having been an imperforate supply of 162, less 90 “returned for perforation”, or 72. The ultramarine shade is particularly rare, as it was only printed late in its usage.
For a brief period in late 1869 and early 1870 the printer of U.S. revenue stamps, Joseph Carpenter of Philadelphia, changed the color of six First Issue stamps including the $15 Mortgage, from blue to ultramarine. The underlying rationale is clear. The Commissioner of Internal Revenue, in his Annual Reports and elsewhere, had expressed concerns about loss of revenue through washing and reuse of stamps. Not only were cancels much more visible on ultramarine stamps than on blue, but the new ink was fugitive; according to Carpenter “it cannot be washed without defacing the stamp.” Astonishingly, Carpenter made this change of his own accord. On October 30, 1869, he wrote new Commissioner Columbus Delano, “Some months ago we commenced the use of inks of a more fugitive nature than those formerly used, desiring to aid the Bureau in the attempts to arrest the re-washing of stamps. … I am aware the new colors did not produce as full and clear an impression; but as they could not be readily washed, I directed their use. … if you direct a return to the more indelible tint, I will of course follow your instructions.” The observed disappearance of the ultramarines after mid-1870 tells us that such a directive must have been received, bringing the brief “ultramarine experiment” to an end.