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Originally Posted by teetwoohsix
Interesting thread, I've been following this and will add some thoughts.
I've always felt the way Rob and Ted have, that sun exposure wouldn't remove all of the red in a card-and, I still pretty much feel that way. I may be wrong, but usually some cards missing red , where you can still see a touch of red (like that Cobb, for instance) can have another explanation.
As you can see in the corner of the Cobb, Chris is right- that corner shows it was tucked in a photo holder, commonly seen in old photo albums where you have one on the upper right, and one on the lower left.
So, I wonder about this- most pages in old photo albums are black. Could whatever they use to dye the pages black react to the red ink over time? That could explain why it did not affect the corner that was tucked, but the bottom of the top page laying flat on the card, over time, reacted with the red ink? Not sure, but something to think about?
The other cards on the montage- can't help but wonder about glue reaction (chemical reaction) on those cards....they all look heavily glued on....
Some people in the past have likened the sun exposure thing to a can that has sit in the sun, and over time the image faded......but, that's an image on aluminum or tin- the sun heats it up a lot hotter than the sun heating up paper? It seems like the sun would heat up a metal more than it would paper? So, I don't think that is conclusive (apples to oranges?).
I think it's possible that the red could dull a little over time due to prolonged sun exposure, but it's hard to imagine it would make the red completely disappear-I would think you would be able to clearly see some of the red still.
Keep in mind, these cards can be soaked and not lose any of the red. It's hard to imaging sun could remove it but water can't.
Again, I may be wrong. These are just my thoughts on this, and I am not a scientist. The Willis portrait is mostly found in red, but you also have many found in this burgundy type of color. Was this deliberate? The Abstein, mostly found in red, but many are found in orange-was this deliberate? Or, did that many Absteins get exposed to sunlight for too long? Sort of seems deliberate to me, because of how many examples have this color of orange. And, this Donie Bush card....look how red it is. Does anyone have an orange Donie Bush card? If so, are there any signs of glue residue on the back?
Sincerely, Clayton
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Sun exposure will fade many red pigments, especially ones derived from natural sources.
Cochineal produces the brightest reds, and sets better than most protein based fibers. In other words It won't easily wash out of wool. It was widely used before cheaper stuff came along, and has made a comeback in food and cosmetics since many of the synthetics are suspected or proven carcinogens.
http://en.wikipedia.org/wiki/Cochineal
The main points
"In artists' paints, it has been replaced by synthetic reds and is largely unavailable for purchase due to poor lightfastness."
"Cochineal is one of the few water-soluble colourants that resist degradation with time. It is one of the most light- and heat-stable and oxidation-resistant of all the natural organic colourants and is even more stable than many synthetic food colours."
One of the replacements for it, Alizarin or Rose Madder, is also not particularly lightfast. But it could be made from coal tar rather than the labor intensive insect harvesting for Cochineal.
http://en.wikipedia.org/wiki/Rose_madder
"As all madder-based pigments are notoriously fugitive, artists have long sought a more permanent and lightfast replacement for Rose Madder and Alizarin"
Those were the two main sources of red in the 1910 era. Both are fine in water, but not great in sunlight. (Sunlight stable reds didn't come along until after 1958)
One of the big surprises in the lot with sun exposure was that the pink which I'd believed to be simply a red mixed with white appears entirely unaffected.
It's possible some chemical put off by the glue or by the cardboard could affect the bright red and other colors. I simply don't know enough chemistry to be sure.
I do know the common red pigments that made up probably around 90% of the red dye/pigment market at the time were probe to fading from light.
So going with the simple explanation seems to work.
I'd be happy to have a real chemist give an explanation either way.
Steve B