Polyurethane and modern human bones

This is a response to Barbara Appelbaum's comments on consolidation
of bone material.  Barbara recommended the use of Krylon products,
Krystal Clear and Water Clear as they contained B-72.  This is
problematic, as I have attempted to discover evidence that any
Krylon product contained B-72.  Krylon Crystal Clear was believed to
have contained B-72 due to reports made in the 1960s by some artists
and conservators referring to Rohm & Haas Reporter 1961.

This is reproduced in the current Painting Conservation Catalogue
(page 138).  I published my findings on tracking down this
information in the AIC Newsletter. Information I received from
Krylon Scientist John Anderson (1993) only B-66 (copolymer of
n-butyl methacrylate and methyl methacrylate) was ever used in
Krylon products in the 1960s and 1970s.  Debra Daly in her most
useful thesis on pastel paintings (1978) makes the reference to B-72
and cites the Rohm and Haas Reporter 1961, v. 19, n2.  I requested a
copy of this Reporter from Rohm and Haas but they could not find a
copy.  This apparently was due to their selling Krylon to Borden.
Rohm and Haas Technical Representative Theresa D. Sims told me in
1993 that all technical data probably went to Borden after the sale.

Rohm and Haas Scientist Paul Pierson told me that Borden sold Krylon
in the 1980s and that he had been unable to find any documents about
Krylon formulations prior to that time.  The Canadian Conservation
Institute (what would we do without these great people) Analytical
Research Services confirms that Krylon was B-66 (1303) ARS report
1615.   These tests were repeated for Krylon 41303 comparing samples
from 1979 and 1987 and the components are the same.

While n-butyl methacrylate has a greater tendency to cross-link in
response to carbon-arc fadeometer exposure than MMA (Feller,
1959;1976;1981) the mixture apparently mitigates this effect.  I
have found B-66 to be soluble after 5 years on painted canvas test
surfaces (Krylon was a favorite of many Beat artists and 60s
artists) and on works painted over 20 years ago.  In a recent study
Jane Down of the CCI found that B-66 yellowed in light aging but was
little changed in samples kept in the dark (personal communication
1993). Feller's studies showed that the main effect is cross-linking
resulting in increasing insolubility in toluene, but in 1993 Robert
told me that the heat from the lamps appeared to have skewed the
results and that lower temperatures showed little crosslinking (I
put this in my 1993 letter to the AIC Newsletter).  Feller, et al in
1981 suggested the addition of an inhibitor and their initial
experiments showed this would work to reduce cross-linking that was
detected.  Nelson and Wicks (1982) extended these studies and found
that there was an optimum amount of inhibitor that could be used.

In 1988 I understand that Canadian conservators were in a dialogue
with Borden officials in an attempt to have B-72 used for Krylon
products, but that Borden sold Krylon before these could result in
any change. CCI tests in 1979 showed that Krylon crystal clear did
not contain inhibitors (ARS 1615).

Niccolo Caldararo
Director and Chief Conservator
Conservation Art Service

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                  Conservation DistList Instance 12:51
                Distributed: Tuesday, December 15, 1998
                       Message Id: cdl-12-51-006
                                  ***