crystallisation in lower layers has been taking place. Moreover, attempts to
avoid crystallisation of salts in the pore water by enhancing relative humidity
of the object has induced enhanced microbial growth, and thereby biodeteri-
oration, in many cases. It should be borne in mind that furniture, painted
sculptures, organs and additional decoration nearby may require a different cli-
mate to that needed to restrict deterioration by soluble salts in the wall painting.
Attempts at environmental control to stabilise mural paintings were used
for the restoration of the paintings in the Tomb of Queen Neferati at Thebes.
In this case, the relative humidity outdoors and in the tomb with different num-
bers of visitors was monitored and compared. The results led to a correspon-
ding restriction in the numbers of visitors allowed into the monument.
Stabilisation by chemical reactions. The so-called Barium method developed
in Florence by Ferroni and Dini is well-established and has proved to be a con-
venient, efficient and durable method of consolidation, after more than 30
years of use. This method depends on the transformation of gypsum. The reac-
tion between ammonium carbonate and gypsum (desulfurication) and appli-
cation of barium hydroxide produces insoluble barium sulfate, followed by a
spontaneous formation of barium carbonate (consolidation). There are well-
known limitations due to the presence of copper pigments as well as some
organic bindings (like animal glue and vegetable gums), which will not tolerate
water from the poultice or undergo cleavage reactions due to strongly alkaline
conditions. Therefore, preliminary testing is essential in the case of tempera
paintings. Best results are achieved when applied to frescoes and lime paintings.
To overcome the restrictions of the Barium method, ammoniumcarbonate
was, in some cases, replaced by anionic exchange resins that are less aggres-
sive and enable the treatment of tempera even in the presence of copper pig-
ments. It must be added that the reaction of anion exchange resins is restricted
to the surface in contact with the resin. Furthermore, the first-stagetransfor-
mation producing barium sulfate is left out and barium hydroxide is applied
directly. This technique is convenient with the many restrictions imposed by
preconsolidation by synthetic resins.
Extraction of ions. Methods to reduce salt loadings were, in the beginning,
more or less restricted to the application of wet compress materials, e.g. cel-
lulose pulp, to the surface of the paint layer. The enhanced humidity leads to
hydration and enhanced solubility of ions that are transferred to the surface, and
migrate into the pulp material by evaporation of water from the compresses.
Repeated applications are necessary and the quantity of ions extracted has
to be measured to decide to what extent the extractions should be done.
Obviously these extraction techniques can only be successful, if it can be
assured that there will be no further transport of ions into the painting, possibly
enhanced by the method of attracting the salts into the compress. Hence the
Wall Paintings: Aspects of Deterioration and Restoration 245