Into the Deep Blue
I have some 40 Cape of Good Hope 1853-64 Triangular Four Pence Blues, and perhaps a third of them show some degree of sulfuretting. Yes- a lot. !! These ugly gray-greenish- brown spots can change the perceived color of the stamp.
I touched on the problem with this post...
..where two stamps (Ex 8 & 9) showed evidence of sulfuretting. I also gave an explanation and details of my understanding of sulfuretting.
As I would prefer, with this blog post, to just do a "show & tell" of some of the sulfuretted stamps in my collection, I will put the chemical explanation of "sulfuretting" at the end of this blog post, if the reader wishes to read it. (The explanations are still speculative, as I have found suggestive, but not definitive literature on the subject.)
And the result was.....No change.!! There was not one bit of difference.
I think we can safely say the stamp was subject to some sort of chemical change, not sulfuretting. (From my chemistry study days, when I see green, I think of copper compounds.)
More specifically, how can the Sulfur compounds Sulfur dioxide (SO2) & Hydrogen Sulfide (H2S) be reducing agents that can change Fe+++ to Fe++?
And how does Hydrogen Peroxide work as an oxidizing agent and change Fe++ to Fe+++?
For those that would like to see the actual chemistry notations, here it is....
Oxidizing agent that can be used in the changing of Iron (II) ions to Iron (III) ions.
H2O2 + 2 H(+) + 2 Fe(2+) Reacts to 2 Fe(3+) + 2 H2O
Reducing agents that can be used in the changing of Iron(III) ions to Iron(II) ions.
SO2 + 2 H20 + 2 Fe(3+) Reacts to 2 Fe(2+) + SO4(2-) + 4 H+
H2S + 2 Fe(3+) Reacts to 2 FE(2+) + 2 H(+) + S