White lead

Robert Mussey <rmussey [at] musseyassociates__com> writes

>I have a superb 18th century Boston, Massachusetts desk with
>interior letterhole compartments retaining original paint with its
>drying oil and white lead, Prussian blue and chalk  pigments. There
>is a later, virtually identical but fairly thin overpaint with
>generally similar pigmentation lying on top of this. Both layers are
>relatively thin, both appear to be heavily cross-linked.
>
>I'd appreciate any suggestions for safe, controllable removal of the
>overpaint. I've tried a full range of solvent gels and mixtures.

It is not clear as to whether "virtually identical" means an FTIR
study has been done and the composition of materials is identical or
if their behavior to solvent testing done appears to be identical.
If the full range of solvent gels have been tried, the next step
might be to try a water based cleaning system. Perhaps artificial
saliva or a chelating agent (like EDTA) gelled. Punch up the pH to
between 9 or 10 and you should be able to compromise the mechanical
bond between the two crosslinked coatings. Swelling the overpaint
may be enough. Back the pH down to where it is just effective and
you should gain a fair degree of control. If the first coating was
crosslinked before the overpaint was applied, there should be no
chemical bond between the two. A dirty surface between the two would
be helpful also. This may need to be done cautiously and with
careful timing. Make certain to clear the surface very thoroughly or
saponification (also known as Arlen-ification) could cause your
original coating to become water soluble.

You could try removal by disadhesion first. Test by applying a
length of tape and rubbing down hard, then pulling off. The overcoat
might come with it. Duct tape works well (conservation grade, of
course).

If all else fails, you might have to resort to a controlled gelled
stripper, like pyrrolidone. However, this would be very tedious,
one inch at a time removal and is risky especially with a very thin
overcoat.

Let me know if anything works, if not, we have other tricks up our
sleeve.

Wendy Leeds
Deller Conservation Group
Geneva IL


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                  Conservation DistList Instance 15:54
                 Distributed: Tuesday, February 5, 2002
                       Message Id: cdl-15-54-003
                                  ***