Matte patina on chromolithograph

I have been asked to offer consultation about a problem with a
chromolithograph varnished with shellac, mounted on a textile
support and I was wandering if anyone has had any similar
experiences and could help me understand what happened.  The
conditions of the item were poor: the paper was torn in various
areas, the varnish had browned and there were small bubbles and
cracks on the surface.  During the conservation process the painting
showed an unexpected matte patina.  Why did it appear and how can it
be removed?

I've been informed that the conservation process employed consisted
of:

    Dry separation of the textile support

    Cleaning of the verso with a scalpel and, only locally, with
    methylcellulose to remove the remains of the adhesive

    Protection of the painted layer with Japanese tissue 5g, adhered
    with methylcellulose

    Ethanol bath

    Elimination of the Japanese tissue: first, failed attempt with
    dry technique, then success with room temperature water bath (15
    minutes) to regenerate the methylcellulose

    Drying of the item: the matte patina appeared during this
    process

    Drop and capillarity tests with water, ethanol, isopropyl
    alcohol, toluene, acetone, trichloroethylene, white spirit.
    They all didn't work;  the latter was able to remove the
    browning but the matte patina increased

Claudia Colini
Assistant Book Conservator
Universidad de GranadaFacultad de Bellas Artes
Avda. Andalucia s/ns
18015 Granada
Spain


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                  Conservation DistList Instance 27:22
               Distributed: Wednesday, November 20, 2013
                       Message Id: cdl-27-22-015
                                  ***