Amber Listserv / epoxy conservation over the years

[Hans Henderickx]

The restauration of f.i. medieval stained glass requires a strong transparant substance that hardens but does not shrink (polyester shrinks while hardening, polyurethane is in a constant shrink while the volatiles evaporate over the years, both these substances are quite weak and can often be scratched off with a nail). The restauration/conservation substance should also have a refractor index close to glass, and stand UV radiation for years. The substance should be capable to follow temperature volume changes without cracking or loosening. At his point only high quality epoxy (f.i. slow hardening restauration Araldite) is suitable and permitted for such glass restauration, and the excellent results on stained glass are known for many years. The more recent results on amber and copal stabilization appear equal, and therefore this system is used on amber by larger institutions, f.i. the Musée National d'histoire naturelle de Paris. Embedded/coated pieces of amber and copal do not show the slightest change after 10 years, and artificial weathering experiments turn out well.

The vacuum method is preferred to make the epoxy penetrate cracks and to avoid air bubbles, I described an alternative method with epoxy dipping of the sample and consecutively mounting in a rotating device while hardening for 24 hours to obtain a homogenous coating in "Mitteilungen aus dem Geologisch-Paläontologischen Institut der Universität Hamburg 98(2005) (A new genus and species of fossil scorpion from Baltic amber (Scorpiones, Buthidae)). The epoxy hardens without cure inhibition after 48 hours to a smooth coating, and it can be grinded and polished as the amber itself. Large Madagascar copal pieces from my collection  became very strong, and don't break any more when they fall.



Hans
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