The Book Switch Theory

[oshfdk]

The signature is indeed visible before chemical treatment, and appears to be the same in all visible aspects. It is very faint though. Its obvious that it is there if you're looking for it, but honestly not that obvious if your attention is drawn to the rest of the content. 

If something is visible on a photograph, especially on a black and white photograph, this doesn't necessarily mean it was visible just as well with a naked eye. B&W photography often employs many techniques to enhance contrast.

As far as I remember, this also was mentioned by Voynich himself, that he first was able to notice the signature on the photograph and only then checked the page. I can't find a source, but Lisa Fagin Davis mentioned this: You are not allowed to view links. Register or Login to view.