T206 Ghost Overprint Back (Fielding)

The images showing above are T206 Beals Becker and Charlie Starr with ghost overprint on card back. These two are the only known specimens with overprint on card back that are in fielding pose.

Each card back has black ghost image of himself and it is the negative image of the card front. The negative black printing is in very fine details and it disproves the possibility of the black ink penetrate the cardboard. It also refutes the odds of the black ink wasn't completely dry during printing process and another cardboard stacked on top and the color transferred onto it.

Two things they are in common are they are both from the 350 Series with Piedmont Back and both players are from Boston Nat'l. If those black printings are the same as the card front, it could be easily explained. But they are the negative of the front images and in such fine details, the cause of these overprints may remain mystery forever.