*****I'd only buy a card with a small card number from a trusted source. It would have to be photo-engraved, with the correctly colored back, and no fluorescing under the black light. If I owned one, I'd authenticate my own like we did earlier in this thread and print my own authentication sheet with the findings.
*****
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These Ruth Candy cards are rare, therefore, there are not enough images to say for sure, but based on the images I've found (Please attach your Ruth Candy card to this thread if you have one so we can figure this out),
1.
Cleveland used white paper, images both black and white and sepia, with sepia images resulting in a slight beige appearance.
2.
San Francisco used brownish paper with black and white images, which caused the black and white image to be beig-ish and somewhat sepia colored (don't have one so it's hard to tell
Therefore, blank backs can be correlated with a particular city if this is correct:
Cleveland's white paper:
San Francisco's brownish paper: