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Subject: Hair Acrylic adhesives

Hair Acrylic adhesives

From: Geoffrey I. Brown <gibrown>
Date: Wednesday, March 29, 1995
Stephen Koob <koobs [at] simsc__si__edu> writes

>Subject: Hair
>
>I question Geoffrey Brown's statement concerning the limited bond
>strength of B-72 to a metal substrate.  In my testings this resin will
>have more than adequate strength, even with use on dissimilar
>substrates. I also question the "greater resolubility" of 3M #4475
>Plastic Adhesive.  What is this material anyway, and on what grounds can
>it be recommended?

At the risk of opening a very big can of worms, I offer the following
response to Stephen Koob's inquiry regarding 3M #4475 acrylic adhesive.
As a preface, I have been involved in formal and informal empirical
adhesive testing for over 25 years and have been able to track the
behavior (aging and reversibility) of a number of materials for most of
that time.  Despite the many published references to B-72, I and many
colleagues have little liking for it as an adhesive.  Its reversibility
in many contexts is very problematic - remember, the original testing of
B-72 was as a painting varnish and the context/methodology of its
reversibility was closely defined only when it was used as a surface
coating.  Most of the acrylics are excellent film-formers, hence,
excellent coatings.  They do not function as well when used as
adhesives.

One of the commercial formulations I discovered in the early 70's is a
product of 3M Company, their #4475 Plastic Adhesive.  At the time, they
were not willing to reveal the formulation other than to say that it was
an acrylic in MEK.  I have used this adhesive since in many applications
and have repeatedly tested its bond strength with a variety of
substrates and its reversibility characteristics over better than 20
years.  Remember also, that many practitioners were using cellulose
nitrate adhesives thru the 70's and 80's despite the obvious problems
that cellulose nitrates created.  4475 was a far better choice than
cellulose nitrate.  Despite the intervening popularity of B-72, 4475
continues to demonstrate superior bond strength on both porous and
non-porous substrates and it reverses more easily, even after
significant aging.

One of the oddities of 4475 is that it darkens in the tube (when very
fresh it is nearly colorless) but it does not darken when dried.
Consequently, one must be careful about keeping fluid stocks too long;
once used, there does not seem to be any further discoloration problem.
As with any material, one must learn the tricks of using it and its
limitations.  I do not, for instance, use it in the manner given in 3M's
instructions, as their technique might result in thicker joints.

Most of us seek to find, or define, panaceas or "standard" materials--it
makes life so much easier.  B-72 has become one of these universal
materials but, unfortunately, B-72 does not do all things equally well.
I suggest that #4475 is a better selection as an adhesive in many
contexts (but not as a coating).  I believe that we must choose the best
material for the job with the greatest degree of long-term reversibility
in the particular CONTEXT.  When choosing conservation materials,
context is, or should be, one of the most important factors.  Both
concepts, reversibility and standard materials, are 100%
context-dependent.

I must admit that I still promote reversibility as a goal, no matter how
illusive, and despite its apparent disappearance from the AIC Code of
Ethics.  I also do not accept the concept of institutionally-defined
"standard materials" which can create a great potential for risk from
irresponsible use on the art and artifacts we seek to preserve, an equal
risk to irresponsible use of "non-standard" materials.

What we are all about as a profession is knowledge, judgement, and
respect for the objects we work on, in full measure without compromise.
I invite Mr. Koob and other interested people to learn something about
4475 and try it out.  It might prove to be a very useful tool for you
and perhaps reduce the need to defend B-72 so strongly.

(I encourage your phone calls to verbally discuss these
issues--313-747-0439 )

    **** Moderator's comments:   and I encourage posting to the list as
    well.

Geoffrey I. Brown
Curator of Conservation
Kelsey Museum
University of Michigan
313-747-0439

                                  ***
                  Conservation DistList Instance 8:80
                 Distributed: Thursday, March 30, 1995
                        Message Id: cdl-8-80-003
                                  ***
Received on Wednesday, 29 March, 1995

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