While it's off topic, this came up in the cleaned with chemicals poll thread and at least one person expressed interest.
A lot of info about fakes and alterations from one of the expertizing groups in the stamp hobby.
I started replying there, but realized it was too far off the topic for that thread so I started a new one.
The Philatelic Foundation is one of the three main authenticators for US stamps, and at the international show in DC in 2006 exhibited a fascinating bunch of fakes and altered stamps. Many done well enough to fool most collectors. They have put a similar display online. As well as an article.
Article about regumming
http://www.philatelicfoundation.org/...been-regummed/
several pages of alterations and outright fakes. Many of them good enough that they'd fool me. I'm getting better, but some of these are very well done.
http://www.philatelicfoundation.org/...and-forgeries/
And a page as an example of why those alterations are done. Scroll down to the bottom.
http://www.philatelicfoundation.org/...2014/02/11.pdf
The 1902 issue coils were a bit experimental and are very rare.
The ones shown
4c brown Normal stamp catalog value used 2.50
A real schermack perf coil CV $50,000
2c imperf CV 35.00 for a pair
2c vertical coil CV $450,000
5c blue normal stamp CV 2.25 used
5c coil CV ---Foolish fakers! it's not known as a horizontal coil.
1c imperf CV 35.00 for a pair
1c horizontal coil CV $16,500 for a pair
2c imperf - CV 35.00 /pair
2c Horizontal coil CV $18,000 /pair
Those are some pretty severe examples, but that sort of thing and more are done.
And an example from my own collection.
3Ct treasury stamp from 1873. The line through the 3 makes it position 80L33 (position 80 left pane plate 33). They were printed in two 100 stamp sheets on one piece of paper and then cut into individual sheets. Position 80 is the last stamp in the 8th row of the 10x10 sheet. It should have a straight edge at the right from where the sheet was cut in two. But since straightedges are less desirable someone tried adding perforations to make it more saleable
Very poorly done, and not likely to fool anyone. What's it worth you might ask?
The catalog value is a whole $2. And they're usually available for about half of that. The variety is only 1/400 stamps since there were two 200 stamp plates, but it's not listed in the catalog and would bring only a small premium if any. Like maybe selling for $2-3 if someone knew what it was.
Steve Birmingham