The VMS ink is NOT iron-gall

[eggyk]

I appreciate all of the answers regarding how the ink interacts with the parchment, thankyou!

There is no contradiction.  The article I quoted says that ocher becomes transparent by 800 nm, while IGI remains visible up to 1200.  The other says that IGI becomes transparent between 900 and 1500.  The VMS images show its ink becoming transparent around 850 nm or so.

All the best, --stolfi

How does this not contradict?

You are basing the claim the the VMS ink is not IGI on the fact that it appears almost transparent at ~850nm, which supposedly shouldn't occur in IGI until ~1200nm according to your linked study. 

But the other study shows that their IGI appeared nearly transparent at around the same range as the VMS ink (~50nm difference, but this is based on the subjective description of "nearly transparent"). Therefore the VMS ink becoming nearly transparent at ~850nm does not necessarily indicate that it isn't IGI.

By the same logic, you should assert that the IGI in the second study is not IGI at all, because it is nearly transparent at ~900nm, while IGI should be visible until ~1200nm. 

I downloaded the images and checked. At 870nm, the text is still faintly visible. At 940nm, the text is fully invisible. This suggests that the IGI became transparent at around ~900nm, which is exactly consistent with the IGI in the second study. 

870nm (file Voynich_17r+MB870IR_038_F)
   
940nm (file Voynich_17r+MB940IR_012_F)