Bureau of Engraving & Printing Vignette Proof, Mixed Flour 1898 var
A version of this die was used for 1908 Series Mixed Flour Taxpaid stamps.
The little known category of tax stamps originated in the Progressive Era as an initiative to protect the public welfare. The target of the tax was ground grain (wheat, rye, barely, etc.) on which the processor could not guarantee the origin of the contents. Thus the sack of flour might have contained mostly wheat flour, but some of it might have come from another grain. The first mixed flour stamps were issued in 1898.