Iron gall ink and discoloration

Florane Gindroz <florane.gindroz<-a t->bluewin< . >ch> writes

>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?

At some time in the past, your manuscript has been treated with a
solution of potassium hexacyanoferrate (III), (potassium
ferricyanide) in order to restore the colour of faded ink.  The
ferricyanide reacts with iron (II) ions from the iron gall ink to
form the dark blue pigment Prussian Blue. While this process can be
successful in reinforcing the colour of the ink (and your
photographs show that this has been achieved), it can also wash the
ink away or cause it to spread, staining the whole manuscript
blue--which your photographs also show.

This process was first described by Charles Blagden in the
Philosophical Transactions of the Royal Society of London in 1787
(vol. 77, 451-457) and was popular in the 19th century, as was the
use of various other chemical reagents, although they were condemned
at the St Gallen International Conference on Manuscript Conservation
in 1898 for causing irreparable damage to manuscripts.

Unfortunately there is nothing that can be safely done to remove the
blue staining.  However, using multi-spectral imaging it may be
possible to capture an image of the original writing.  See Robert
Fuchs, "A history of the chemical reinforcement of texts in
manuscripts: What should we do now?", Care and Conservation of
Manuscripts 7 (2003) 159-170 and plates XXVI - XXX.

Barry Knight
Head of Conservation Science and Research
The British Library
London


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                  Conservation DistList Instance 27:41
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