"The story of "La Belle Ferronniere" is as much about the aesthetic and scientific foundations of modern art history as it is about the authenticity of the painting itself."

[joseph berg]

Isn't it possible for "lead-tin yellow" could be added to a modern forgery
to make it seem older?:

http://www.artknowledgenews.com/2010-01-30-22-26-11-disputed-da-vinci-portrait-sells-for-1-5-million-at-sothebys.html