Hi lockumupthrowawaykey
To get more information about seebecks take a look at the APRL (American Philatelic Research Library):
http://www.stamps.org/InmagicGenie/...RY&Type=opacI believe the book by Robert A. D'Elia and Douglas B. Armitage is one of the latest. A friend has the book and says it is excellent:
http://www.stamps.org/InmagicGenie/...RY&Type=opacIf you are not an APS member you may be able to get a book, or manuscript, through the inter-library loan system. Check with your cal library.
I had a friend who once told me that if the issue looked too clean and pristine it was probably a seebeck. I have a ton of these issues for Ecuador.
Jerry B