Modigliani drawing

I have been examining a blue crayon drawing by the artist Modigliani
dated c.1913 from his Caryatid series that has become unevenly
discoloured. Across the centre of the drawing, on recto and verso an
opaque white substance has been applied to cover staining. There is
generalized discolouration as well as darker, vertical linear stains
at regular intervals. From the verso the staining that is not
covered does not appear particularly dark and disfiguring in
comparison to the stark white appearance of the covering material.

The hand that has applied the covering material has avoided the
crayon lines, but has covered the more subtle smudged shading. The
application of this substance does not follow the design of the
drawing in any way. I have had samples of the covering material
analysed and it was found to be lithopone, a mixture of barium
sulphate and zinc oxide often used in poster paints and cheap
watercolours.

During my investigations I have discovered another drawing in the
literature, in this series, where a white substance appears to be
covering accidental marks.

I am considering removing the white covering substance, of course
without disturbing the paper surface, or media on the recto, but I
would first like to ask,

    1.  Has anybody had experience with treating Modigliani drawings
        from this series?

    2.  Has anybody come across Modigliani drawings that contain
        white paint that does not fit in with the design and appears
        to be applied to hide staining?

    3.  Has anybody had experience with removing lithopone from
        early 20th C. machine made paper?

I am aware that removal of the substance may reveal that the paper
is lighter in tone in this area and that the staining may be more
disfiguring than I anticipate but my examination suggests that the
contrast would not be as great as that between the lithopone and the
paper colour.

I would greatly appreciate any comments people may have on this
subject.


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                  Conservation DistList Instance 17:8
                   Distributed: Tuesday, July 1, 2003
                        Message Id: cdl-17-8-012
                                  ***