The 6-cent stamp joins the 3-cent as an orphan of the Issue, paying no single rate by itself and possibly carried over from the 1890 Issue as a contingency against a postal rate increase. Should the first-class rate increase to three cents, this stamp would have paid the double rate. It is, however, of interest that the earliest known usage of any First Bureau postage stamp is associated with this stamp—August 11, 1894.
The unwatermarked first printings were produced in an unattractive dull brown. The second printings followed on watermarked paper in a similar dull color. The U.P.U. printings upgraded this color to quite pretty shades of lake and claret in December 1898.
Sometime during the second printing period an unknown quantity of stamps was printed on paper watermarked “USIR” (U.S. Internal Revenue) instead of “USPS.” Only about half of these stamps could ever be identified because of the “I” or “R” watermark, the “U” and “S” being identical. This error is extremely rare in used condition and only recognized in a handful of copies in mint condition, but with a little luck, more might be found!
The unwatermarked printing can also be found in the vertical format, imperforate horizontally. Like the 5-cent, it is extremely rare in this variation.