This Spirit Of The Past is an extremely rare, one-of-a-kind Goldtone originating in the Seattle Curtis Studio.
In all other extant printed examples of Spirit Of The Past - Apsaroke, the mounted group faces left. Only in this unique Goldtone is the group facing right.
The negative was not flipped when this Goldtone was made, the signature and copyright insignia in the image are properly placed in the right-hand corner, not reversed.
Rather, I believe this to be a one-off experimental Goldtone print made in Seattle some time prior to 1919.
Additionally, this Goldtone is one of the only 15 percent that were produced by Curtis which had both perfect exposure and a flawless emulsion, free of any imperfections in the emulsion, no finger prints or flaws whatsoever. The image itself is luminous, neither too dark nor too light, representing the perfect and most desired exposure to be found in the Goldtone process.
Curtis produced very few photographic works that were unique, this is a rare opportunity to acquire one of them.