Colorization - what was it's purpose?

[Jorge_Stolfi]

But all those pigments are naturally-occurring minerals that don't need any "alchemical" processing other than grinding. And anyway,alchemists would have been unable to make azurite or orpiment.  Even today they require special lab equipment.

That is simply  not correct. Medieval manuscripts contain entire chapters on chemical creation of paints [...] they knew quite well  orpiment manufacturing- not only grinding of material but using furnaces, crucibles and distillation. Check this You are not allowed to view links. Register or Login to view.

I was indeed wrong about orpiment (i confused it with You are not allowed to view links. Register or Login to view.).  And there were indeed other synthetic pigments used at the time, like lead white, minium, and the green that McCrone called "atacamite".  But I stand about the other pigments you listed: they were natural minerals, not made alchemically.  

And anyway McCrone did not detect any orpiment or minium.  On the other hand, they were unable to identify the main green paint and suggested that it was synthetic.

You do not need to go far but see the "pharma" part of VM.

There is nothing in the Pharma section that suggests alchemy.

Here is important to say that the fact that Voynich contains this pigments is another evidence for its authenticity.

Apart from the unidentified green pigment, and the highly dubious identification of the text and drawing ink as iron-gall, all other pigments identified by McCrone were natural minerals that have been available all the time to this day.  Thus the pigments do not give any information about the dates of writing, drawing, and painting.  

I personally believe that the VMS is not a modern forgery, and I am satisfied that that the brow-ink drawings and text date from the 15th century.  On the other hand I see good evidence that the color paints (except maybe for the ubiquitous very light transparent yellow, but including the red text of f67r2) were applied after the book was bound, which must have happened after the Author was no longer around -- possibly as late as 1600 or thereabouts.  I am not aware of any evidence for the thesis that they were contemporaneous with the text and drawings, or that the colors were specified by the Author. Thus any interpretation of the drawings that depends on the colors is probably spurious.

I think that the date of the painting could be even later than 1600, except that I doubt that it could have happened while it was in the Jesuits' possession.  (On the other hand, I see a non-negligible probability that the VMS we know is not the book that was sent by Marci to Kircher; in which case any date up to 1911 would remain possible.  But this is the topic of another thread.)

All the best, --stolfi