[split] Jorge's Retracer Thread: darker ink, retracing of text and drawings

[Jorge_Stolfi]

I will keep naively assuming that the people at McCrone know what they are talking about.

As you wish.  But I have read the full report, and I do understand the physics and chemistry that they used (or not).  The raw data is very useful and seems reliable, but their interpretations of it are not. You need not believe, but the report has several bloopers and makes claims that are not supported by the data -- including the conclusion that the ink is iron-gall.  Even when their instruments did not detect significant amount of iron. 

But that is not important.  More important is the claim by other experts, who were specifically trying to distinguish iron-gall from ocher in the underdrawings of paintings by using multispectral imaging.  They say that iron-gall ink is opaque to infrared up to 1200 nanometers and beyond, whereas ocher becomes transparent  above 800 nm or so.  And guess what one sees when comparing the 800 nm and 950 nm images of the VMS...

All the best, --stolfi