Synthetic resins

Ian Nurock <inurock [at] yahoo__co__uk> writes

>... I will be comparing Paraloid B72 to a few
>dispersions: Primal B60A, Primal (Rhoplex) AC-33, Primal WS24 and
>Rhoplex AC-234. I will be asking the question why B72 has become so
>popular with conservators when in some cases other polymers are just
>as adequate? ...

I am glad you are doing this study.  While B-72 has many admirable
qualities, it is often not the best choice in many instances.  It is
always good for conservators to have many arrows in their quiver
from which to choose. However, I encourage you to make sure you
thoroughly drive off all solvents before drawing any conclusions.

Many adhesives, particularly emulsions and dispersions, and those
containing slower-evaporating solvents do not fully set for many
weeks, and therefore do not display their true natures until long
after they have been used.  Many acrylics, especially, seem to be
tough and flexible at first, only to slowly become extremely brittle
with time as the trapped solvents slowly volatilize.  An incubator
or low temperature oven can help fully set these adhesives in a week
or two.

Of course, it is equally important to make sure a very porous
substrate like plaster is sealed properly before bonding, or very
weak joins will result no matter what adhesive is used.  Then of
course there is the issue of long-term yellowing and diminished
reversibility.  I believe B-72 still has the best proven track
record in these areas and so it is often the first "go to" adhesive
where those qualities are especially desired.

Good luck with your study,

Linda Roundhill
Art and Antiquities Conservation, LLC
Woodinville WA
USA


                                  ***
                  Conservation DistList Instance 25:27
                Distributed: Saturday, December 3, 2011
                       Message Id: cdl-25-27-001
                                  ***