Iron gall ink and discoloration

At the Bibliotheque de Geneve we've got a manuscript on vellum on
which someone used a solution applied with a brush probably in order
to improve the contrast of the iron gall ink (or to copy the
manuscript?).  Now the surface is light blue and the ink dark blue.
However, in some parts it became hardly readable (conglomerate).

Does anyone know about this phenomenon and know how it could be
reduced?

You can see some at

    <URL:https://www.dropbox.com/sh/mpaw22455jk4hg3/tuEfxTgG26>


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                  Conservation DistList Instance 27:40
                  Distributed: Friday, April 18, 2014
                       Message Id: cdl-27-40-013
                                  ***