New video: "Is the Voynich Manuscript fake?"

[asteckley]

Let me share what I know of the chemistry involved. 
 ...   
that could explain why McCrone detected titanium, but not titanium white, in sample 17. ...

Jorge, your detailed description is very helpful. If I understand correctly though, you are suggesting that the presence of titanium is consistent with a pre-modern ink based on natural brown pigments (like sienna or roasted ocher) rather than iron-gall ink, because these minerals may often contain titanium as an impurity. That theory would indeed account for the element's presence without implying modern materials like synthetic titanium white.

You are correct that the McCrone analysis seems to have seen no titanium white. And the distinction  is indeed crucial –  titanium white is titanium dioxide (TiO2) in a specific crystalline form (anatase), which, when synthetic, suggests a post-1900s origin as it did with the Vinland Map. 

But the McCrone report states "Titanium compound" for Sample 20 and "Titanium compound (particle)" for Sample 17.
Generalizing that finding as a common impurity minimizes the analytical weight given by the report's language and it ignores the expected protocols of a report from a professional source like McCrone.  They were specific in their terminology.  As one expects in a report from a professional laboratory like McCrone, they use explicit qualifiers when constituents are present at low levels, such as "Iron gall ink (very low iron)" , "Cuprite (minor)", or "Azurite and cuprite (traces)", etc. The fact that the McCrone report listed "Titanium compound" for Samples 17 and 20 without any such qualifier (like "trace" or "minor") strongly suggests that the titanium was present at a concentration deemed significant and measurable by professional analysts.

We have to acknowledge that the McCrone report explicitly identified a "Titanium compound," which, despite not being identified as (and likely not being) a specific crystalline form of "titanium white" raises a distinct inconsistency with the expectations of a medieval source for the pigment. (Attempts to get an explanation for this inconsistency from McCrone and other sources at Beinecke have failed).

I know that others have also attempted to claim the presence of this titanium as a common, insignificant impurity, but it seems to be driven more by a desire to explain away the element rather than to treat the evidence objectively. The analytical fact of a significant, unqualified "Titanium compound" finding has to be addressed without being generalized away.