The VMS ink is NOT iron-gall

[Jorge_Stolfi]

The following article shows iron gall ink as nearly transparent in 900-1500nm:  ... Quoting from the article: 

The underdrawing materials that become transparent, and are not therefore visible, include red Conte crayon, charcoal and iron gall ink.

Yes, but that is what the article I quoted said too: iron-gall ink remains opaque up to 1200 nm, while ocher becomes transparent by 800 nm.  And the VMS ink is already transparent before 940 nm (the longest wavelength used in those images).

All the best, --stolfi