Parchment charters

I am working on a damage assessment/inventory of a collection of
parchment charters (13th - 17th century).  Amongst the various types
of damage there is one I can't explain.  On a few charters a brown
discoloration is visible.  It seems as if (a part of) the written
part of the parchment is smeared with some kind of aqueous product.

I am aware of earlier methods to re-visibilize fainted writing ink;
that is I know about this from professional literature.  A 2%
solution of tannin, 5% potassium ferrocyanide, 1% solution of
ferrosulphate, 5% solution potassium sulphocyanide, sulfur ammonium
vapour; in the past it was all tried with or without success.  A
particular side effect of tannin solutions was already known in the
19th century: browning of the paper or parchment that was treated.

Is it possible to determine (without chemical analysis or other
'high-tech' methods) whether a charter is treated with these kind of
chemicals? Has someone seen this type of damage before and how was
the damage labelled then?

You can see a picture at

    <URL:http://tinyurl.com/cgxt2ze>

Cor Knops.
Knops Boekrestauratie
Groenstraat 8
6151 CS Munstergeleen
Netherlands
+31 464200024
+31 623533101


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                  Conservation DistList Instance 26:40
                   Distributed: Monday, March 4, 2013
                       Message Id: cdl-26-40-015
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