The VMS ink is NOT iron-gall

[Jorge_Stolfi]

Is there a test that would beyond reasonable doubt confirm for you that some writing is in iron gall ink?

And is there a test that would beyond reasonable doubt confirm to you that some writing is not iron-gall ink?  When it is you who define "reasonable doubt"?  

Seriously, AFAIK there is no non-destructive test that would positively identify iron-gall ink on a manuscript.  It is an amorphous polymer consisting of an irregular 3D network of You are not allowed to view links. Register or Login to view. molecules (which are themselves quite variable) joined by iron(III) ions.  X-ray diffraction should not give any characteristic signal, and X-ray fluorescence would only say "it contains iron, carbon, oxygen, etc.  

A high-resolution infrared spectrum (Raman spectrum) could detect specific bonds and sub-units in the substance, like carbon-oxygen, maybe the benzene rings; and that could prove that the polymer units are tannin molecules.  But I don't know how big of a sample that would require.

But I would satisfied with a moderately detailed absorption spectrum in the range 700-1500 nm, that, compared to spectra of writings that are certain to be iron-gall (not just assumed) and certain to be ocher, can only match the former and not the latter.

I suppose that a "slightly destructive" test could be to shine a thin laser beam onto the writing, enough to break down and vaporize the tannin, and analyze the fragments with a mass spectrometer. 

Another "slightly destructive" test is simply to try to wash off some of the writing by rubbing with a wet Q-tip.  Iron-gall should not budge, while ochre or sienna (or any of the colored paints and inks) should soften and come off almost completely.  (And I am confident that the VMS ink is not iron-gall because this test has already been made by accident, e.g. on f103r.)

There are simple chemical tests that could positively identify iron-gall ink.  But they would probably require scraping off several words worth of text.

All the best, --stolfi