Faience

Karen Wilson wrote regarding  the treatment of a small Egyptian
faience pot which has previously been reconstructed using animal
glue and small areas of painted plaster, which  is developing salts
and has a sticky residue on the surface.

Whilst it is often impossible to restore the appearance of a
deteriorated faience surface without compromising the integrity of
the object, there is plenty that can be done to conserve faience
objects with a variety of problems.  In this case, it would seem
likely that the combination of the original construction of the
piece, the application of plaster and possibly the storage
conditions may be more responsible for the salts developing than any
pollution.

Cleaning can often be effected with with barely moist swabs of an
aqueous solution of a non-ionic detergent, or a mixture of a
miscible solvent such as acetone or industrial methylated spirits
and distilled water (usually in equal parts). The addition of a
small amount of calcium hexametaphosphate to the solution can
sometimes help to reduce hard concretions on the surface. Careful
testing is of course necessary before applying any solution to the
object.

If the object is very fragile, consolidation with a 5-15% solution
of Paraloid (Acryloid)  B72 (an acrylic copolymer of ethyl
methacrylate and methyl acrylate) in acetone may be needed. Allowing
the solvent to evaporate slowly by keeping the object in a sealed
container helps to encourage penetration and even consolidation and
prevent darkening of the surface, although a slight darkening may
return the surface to a more accurate representation of its original
appearance, as deteriorated faience is often paler than the
original. Further applications may be necessary and more viscous
solutions can be used to bond cracks or strengthen very weak areas.

If the salts are soluble in water it may be possible to remove them
(if necessary) by soaking in changes of distilled water, either
before or after consolidation with Paraloid B72. Bear in mind that
if the object was so fragile that it had to be consolidated before
soaking to remove salts, it may need further applications of
consolidant (after thorough drying) to replace gaps in the matrix
left by the removal of the salts. Some salts will of course be
removed if the object has been immersed in a consolidant, since many
salts soluble in water are also to a lesser degree soluble in
acetone.

In some cases we have treated objects so fragile that even after
consolidation they could not withstand desalination by soaking. The
majority of the salts were removed from the surface with swabs of
distilled water, but any remaining salts in the body had to be left
and the prevention of further crystallisation managed by the use of
a controlled environment, free from organic acid vapours which may
have led to the production of larger salt crystals (e.g
chloroacetates).

Careful testing is required before proceeding with each stage and
the usual health and safety precautions must be observed when
working with solvents and when dealing with the solid Paraloid resin
(which can form a dust hazard in large quantities).

Richard and Helena Jaeschke
Archaeological Conservators


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                  Conservation DistList Instance 13:52
                  Distributed: Friday, April 21, 2000
                       Message Id: cdl-13-52-004
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