170 Chapter 7
2.7 Conservation Materials: Coatings, Consolidants, Adhesives
The most effective preservation method for corrosion-sensitive glasses should
aim at the direct protection of the surface by sealing it with a coating against
the impact of the environment. Organic natural and synthetic polymers (such
as waxes, epoxy resins, polyurethanes, acrylates) have been used for this pur-
pose in the past. However, the coatings have failed in many cases due to their
poor adhesive properties for weathered-glass surfaces and their insufficient
aging properties (see Figure 10). Although an improvement was proposed
based on the application of silane coupling agents, modern conservation
practice favours preventive conservation to avoid the long-term risk related to
the application of protective coatings.
Whereas protective coatings are meant to seal the surface against further
weathering, consolidants are applied to strengthen porous structures of endan-
gered paint layers on glass (see Figure 6) or to deal with fragile archaeological
glass surfaces (Figure 7). In these cases, a consolidation might be necessary
to preserve the original design and thus the authenticity of the object. A risk
assessment is required for each individual object to justify a treatment with a
polymer, since the general requirement for the reversibility of any conservation
treatment is not met in the case of fragile, porous surfaces. At present, several
cellulose derivatives, epoxy resins, silanes, silicones, heteropolysiloxanes and
vinyl polymers are under investigation. Paraloid B72 is the most commonly
used polymer for paint consolidation, being an acrylic resin, applied in vari-
ous organic solvents (such as toluene) in a broad range of concentrations
(3 up to 30 mass%), depending on the purpose of the treatment. Consolidation
under reduced pressure might be necessary to improve the penetration of the
Figure 10Archaeological glass with coating: after several years of exposure indoors, the
polymer lost its adhesion to the glass support