Removing varnish with triammonium citrate and isopropanol

I have recently conserved a series of paintings which were coated in
a discoloured varnish that was insoluble in propan-2-ol, acetone,
I.M.S., toluene, xylene and ammonia solution (pH 9). I eventually
discovered that the varnish could be successfully removed using
triammonium citrate (2% w/v in deionised water), cleared with
propan-2-ol. (The varnish was insoluble when triammonium citrate and
propan-2-ol were applied in isolated steps). It proved vital to the
successful removal of the varnish that propan-2-ol was applied
whilst the triammonium citrate was still wet. Therefore water or a
wetting agent seemed an important reaction condition. From my
observations I think the triammonium citrate had either acted
initially as a base and formed a salt with the aged, acidic, natural
resin varnish, or as a chelating agent and formed a complex with a
source of metal ions (found within dirt or certain pigments) below
the varnish layer.

I think the first suggestion is the most likely because large
passages of paint containing green and blue pigments (possible
sources of iron, copper and cobalt ions) remained unaffected by the
varnish removal process. Then propan-2-ol (a more polar solvent than
water), may have then cleared the triammonium citrate salt or
complex that had formed and thus remove the varnish. I have never
heard of this method being used to remove varnish and would
therefore be interested to hear from anyone who has or can further
explain how it works. Apart from the obvious observation that
triammonium citrate and propan-2-ol may be a potentially useful
combination when removing varnish, I think this observation may also
raises questions about the ability of water to effectively clear
triammonium citrate from the surface of paintings.

Jevon Thistlewood
Painting Conservator
International Fine Art Conservation Studios
43-45 Park Street, Bristol, BS1 5NL, UK.
+44 117 929 3480
+44 117 929 3988
Fax: +44 117 922 5511


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                  Conservation DistList Instance 15:63
                  Distributed: Tuesday, March 19, 2002
                       Message Id: cdl-15-63-001
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