Italy 1926 - Printing Error Or Colour Changeling?

I recently bought a large lot of old Italian stamps. This is possibly the most interesting item I've noticed so far. This is the 25c olive-green and green issued in June 1926 (Sassone 200) as part of the Floreale definitive series.

The stamp is shown on the left is the way it's supposed to look - that on the right is an example that is missing the olive green.



This is a larger image of the stamp on the right:



What I'm wondering is whether this stamp is a case of a printing error (olive green colour omitted) or a colour changeling. Is it possible that at some stage the stamp was washed in something that made the olive green ink dissipate entirely? What do people think?

I think the washing out of the remaining green makes fade/soak/chemical something the most likely answer.

Cjd, that's the nub of the problem. I have 7 other examples of this stamp and after looking at them I find such variation that it's not at all clear to me that the remaining green in the stamp on the right does have a 'washed out' look:

http://www.freeimagehosting.net/ima...1ce1e824.jpg

So this could just be what the stamp looks like without the olive green printing.

Some of the loss of detail in the outer ornaments may be due to plate wear. These lighter detail lines are cut shallower than the other lines. I don't know enough about the ink used on these issue to comment about their stability. Many ealier inks did fade and change color especially where applied very thin such as in worn plates.

Green inks seem to be particularly unstable. I've noticed that in the case of an Edwardian issue from Hong Kong in which the green colour has changed so much that it's sometimes taken for an uncatalogued variety.

However, I've never seen a colour 'fade' to invisibility. It's always possible, of course, but it seems highly unlikely to me.

The U.S. 1851 3 cent ia the most note U.S. stamp for plate wear. The ink used is know to oxidize but does not tend to fade badly. In the worn plates large amount of the design is literally invisible. Under 30X mag the impressions are normally at least partially visible. Can you see signs of the impressions under magnification?

Russ, I can, but they're very, very faint.

I'm with Cjd, the original emerald
has turned almost to turqoise.
A hot water bath may have been the culprit.

Well, it's definitely not emerald, that's for sure - but it also seems too bright a green to be a case of fading. Some of the stamps shown in this bunch (those hosted offsite) are actually paler than this one (although more emerald).

@jimjamtwo... I've got a pile of these stamps too. If I'm not completely mistaken, Your "mystery stamp" is bluegreen/lightgreen color variation (Michel #240b). It's slightly harder to come by than it's darker looking cousin, but still very common (both variations are of minimum catalog value).

That's good to know,
I have the same print variety duo then with the 75c scarlet.

Thanks for the info, scb.