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Subject: Structural support for mural panels

Structural support for mural panels

From: David W. Erhardt <wde>
Date: Thursday, July 16, 1998
Re: Resin soaps
I would like to respond to Mr. Stavroudis's recent posting regarding
a comment by Mr. Caldararo. Mr. Stavroudis objected to Mr.
Caldararo's characterization of my (and Dr. Bischoff's) work as
showing that Wolber's cleaning materials left insoluble films on the
paintings. I agree that the term "insoluble films" may be a bit
imprecise, most of the residual resin soaps are absorbed into and
remain in the paint film itself. The amount that remains on the
surface has not yet been determined; the soaps do, however, have
measurable effects on the surface and appearance of the paintings.
These effects were one of the foci of my work (Studies 39 1994-3-27
is the primary article and the one to which Mr. Stavroudis refers.).

Mr Stavroudis refers to his letter in Studies. I suggest that
interested parties also read my and Dr. Bischoff's replies in the
same issue (Studies 40 1995-210-212). I also recommend Mr. Wolbers's
letter and my reply in Studies 39 1994-284-286. My comments,
especially those regarding the issue of proper clearance raised by
Mr. Stavroudis, still apply.

My study was designed to examine a number of the effects of resin
soaps and their components, not just to determine whether or not
they leave residues. That was not necessary. That the soaps leave
residues had already been conclusively demonstrated by Mr. Wolbers
in his article in Cleaning, Retouching and Coatings, the Preprints
of the 1990 IIC Brussels conference (pp. 119-125). In his study, he
showed that, depending on conditions, between 7-50% of deoxycholate,
30-80% of Triton X-100, and 30-90% of palmitate soaps were left
behind as residues, not after just simple clearance, but after also
soaking in a strong aromatic solvent. It is also of note that the
amount of residue increased dramatically when changing the
counterion from sodium to triethanolamine (or similar amines). This
implies that it is the TEA dragging the "soap" into the film, rather
than the other way around. This fits in with my conclusion that TEA
was the most active component of the tested formulations. The
amounts of residual TEA were not measured by Mr. Wolbers, but they
must be at least as much as the soap anion, and probably much more.
TEA is, after all, a powerful solvent used in excess in the
formulations and capable of acting on its own. It is also, like the
soap anions, effectively nonvolatile.

The implications of leaving nonvolatile residues, especially liquid
ones, in paint films are clear when one considers the continuing
problems caused by Pettenkofer's use of resin soaps over a hundred
years ago (See, e.g., Schmidt's article in the IIC Brussels
Preprints, 81-84.).

My conclusions were not based solely on the data presented in the
article. In addition to Mr. Wolbers's study, numerous other studies
were cited, and others have been published since that support
my conclusions. There is no work that I know of that contradicts my
conclusions. And I should point out again, as I did in one of my
letters to Studies, that it is not up to me or anyone else to prove
that the soaps are not safe, but to those who advocate their use to
demonstrate that they are. So far this has not been done.

Finally, I agree with Mr. Caldararo, especially that more research
is needed.

I would be happy to discuss this or any other matter. My phone
number is 301-238-3700 ext. 116, my E-mail is wde [at] scmre__si__edu

David Erhardt

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                  Conservation DistList Instance 12:11
                   Distributed: Friday, July 17, 1998
                       Message Id: cdl-12-11-003
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Received on Thursday, 16 July, 1998

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