Silicone rubber as an adhesive

Emily M. O'Brien <emily [at] ranches__org> writes

>I am currently treating an archaeological low-fired ceramic vessel
>that was previously assembled using a white, rubbery material.  An
>isolating layer was not applied to the break edges before the vessel
>was assembled.  I tested the adhesive, and its Fourier Transform
>Infrared Spectra was almost identical to that of Dow Corning RTV
>3110 silicone rubber (Catalyst 1).  My questions are, how stable is
>silicone rubber over time?  Is there a possibility that ceramic in
>direct contact with silicone rubber may be harmed by it?  Will these
>joins fail at some point, causing damage to the vessel?  I'm trying
>to decide if I should disassemble the pot in order to remove the
>adhesive or if I'm better off just leaving it be. In addition, what
>would be the best way of disassembling the vessel if that choice is
>made?

Unfortunately, I too, have seen ceramics joined with silicone
rubber. Generally the joins are poor, owing to the high viscosity of
the rubber, and the joins are very difficult to take apart. You can
try David Erhardt's recipe in "Removal of silicone adhesives",
Journal of the American Institute for Conservation, 22, 1983, p.
100.  You will need to wear gloves and have a good fume hood, and
double-bag the ceramic in the solvent mixture. As to the stability
of silicone rubber adhesives, I can only say that I have seen some
discoloration (yellowing) of the white rubbers, and slight
embrittlement within 20 years (compare the silicone rubber caulking
used on your bathtub). I do not know if long-term stability tests
have been carried out. I think you need to assess the stability of
the ceramic, and decide whether it needs re-treatment.

Stephen Koob
Conservator
The Corning Museum of Glass
One Museum Way
Corning, NY 14830
607-974-8228
Fax: 607-974-8470


                                  ***
                  Conservation DistList Instance 16:35
                 Distributed: Monday, November 25, 2002
                       Message Id: cdl-16-35-004
                                  ***