2c Small Queen Unusual Blue Color?

Actually it's green PLUS yellow make blue but that's not how this happened anyway.

Blue like this...?...HAHA

I think you're a bit mixed up here.

Blue (cyan) + yellow = green. Not the other way around.

In regards to your stamp, this is what I see in my 1989 scott's catalogue, 36d blue green (Montreal)
36ii blue green (Ottawa)
Hope this helps!

Hello, I ve put a better picture of my stamp (near a 5c grey small queen). What do you think? It seems to me reasonable to think it s not an alteration. It s far from the picture of the blue-green on this thread (if you have a better pic, please send it).

I was surprised to see a Scott # 36 with such blue color. I checked in my R. Morris Guide (Color Guide for Small Queens, bought recently, and Morris does dot include this "blue" in his Scott # 36 palette ....did scan it but the result was not a true representation of Morris's Guide (there are 3, covering 36-38-42; 35-39-43-40-45;37-41)- so I did not import it on this post.The blue greene and deep blue greene as shown in Morris's # 36 guide looks a lot greener than the examples shown as blue by some members, Kasby being the last one.

John Hillson, in his guide to identification of small Qeens printings, also does not mention a 2c blue in 1st Ottawa, Montreal or 2nd Ottawa printings

Richard Morris, in his 3 guides discusses names given by 3 references on the 2c colours:

I agree with Stallzer and firstfrog2013, it's a changeling. I've also seen blue ones like this in old collections.

Copper or its compounds were used to make green pigment for ink for a long time and I think is still often used. Note old copper pipes in the house start to accumulate green crud; that's the copper oxidizing, copper rust, if you will. Left a longer time, the crud turns blue; it's now a different copper compound. Here called verdigris, see the progress pictures at the bottom showing the change from copper to green to blue:
https://travelingscriptorium.librar...7/verdigris/

So the blue small queens were greens that were in a somewhat acidic environment at some time. The change could be just from bad storage but with gas or coal heating and lighting, there was probably some sulfur/sulfur compounds in the fuel. Sulfur reacts readily and the result is sulfuric acid.

So there's your acid to oxidize your stamps, the factor I believe to have caused a lot of the changelings in 19th and earlier 20th century stamps. Verdigris-based ink is not particularly stable for the long term either. The acid was not enough to kill you but would slowly destroy your drapes and carpet, it would accumulate on album pages and in the air in storage areas where say, old covers might be bundled.

So everyone who likes ink shades (I sure do) has to wonder: Is the shade I have just a product of chemicals in the environment? And how stable is it?

Thank you for these replies. About the oxidation of the stamp, see this: http://www.stampboards.com/viewtopi...0707#p434088
It s an oxidation using a basic component bleach. Now, hybrasil is speaking of an acidic oxidation. Can anyone try the acidic oxidation ? Ok I think I ll try, I just need another 2c small queen :) And I ll tell you...