What Is The Difference In These Two 206-S?

The one on the right is obviously brighter, both ink and paper. I've noticed that most of the 206s I see are more like the one on the left. I wonder if this is a result of different paper or ink at the time of printing or if one has maybe been exposed to more light? I think there is a legitimate difference here - not just a result of different conditions over the years. I'd like to mount both of these in my album, but would like to identify the difference. Are these separate shades?

(Please spare me the "these stamps are 139 years old and it is futile to try to identify shades" lectures. If you legitimately think the difference is a result of differences in long-term storage for these stamps, then cool, but please don't just throw your arms up and tell me it that it is useless to try to understand the ink and paper differences in these stamps.)

Philazilla....Im sure you know.
According to SCOTT there are 4 shades listed for #206.
grey blue
ultramarine
dull blue
slate blue
My guess for your 2...
LEFT :grey blue
RIGHT : slate blue

I find stamp shades to be interesting and challenging. The best you can do is make educated guesses. Even the expertizing agencies are inconsistent, at best, at identifying shades. In fact, the one on the right has a 1995 PF cert that says "Gray Blue." I have a copy of _Encyclopedia of the Colors of US Stamps_ by R.H. White (1981), and the closest color-plate match to the stamp on the left is "pale ultramarine" (206a which isn't even listed as a variety any more) and the closest to the stamp on the right is either "gray-blue" or "dull slate-blue."

The stamp on the left paper appears to me to be toned, making it a bit more yellow. This 'background' hue can influence our eyes a bit when we try to compare the two stamps.

For example, the bottom image shown here is your right hand stamp color applied to your left hand paper.

Even though it is the same (right hand design layered onto the left hand toned paper) note how the blue now appears to be different color from the original right hand stamp. This is all due to the background color influencing our eyes.
Don



To demonstrate how much the background color can influence our eyes, here is an image; the horizonal gray bar is exactly the same color across the entire face of it. Yet our eyes trick us into seeing it with a gradient, getting darker towards the right (it is not, it is the same color).


Gray bar shown here is exactly the same as the gray bar above.

Interesting. I'll play around in photoshop a bit and see what else I can learn.

Have you tried examining them under LW UV? If not that is where I would go next. LW UV can be very good for discriminating paper and ink varieties.