Pigments & Dyes in Middle Ages

This paper presents the outcomes of a restoration project started from 2009 and finalized
in 2011 at the Pīr-i Hamza Sabzpūsh tomb of Abarqū, central Iran. The project comprised of
analytical studies and restoration works on the architectural decorations of the tomb consisting
of wall paintings and polychrome stuccoworks. Micro-Raman spectroscopy (μ-Raman)
and micro X-ray fluorescence (μ-XRF) analysis were used to compare the chemical and
mineralogical composition of the pigments used in the wall paintings and the stuccoworks of
the mihrab. The results showed that atacamite, huntite and ultramarine were green, white and
blue pigments respectively used on both wall paintings and the stuccoworks of the mihrab.
Furthermore, while red lead was used as red pigment on the mihrab, the red pigment of the
wall paintings was identified to be red hematite. In addition, the patterns of the wall paintings
were delineated with a black paint composed of carbon black. The different trace elements
associated with the paints established different sources of supplying pigments used in the
decorations. It is also shown that red lead was partially blackened likely due to the action
of air pollutants. Moreover, an omitted part of an inscription of the mihrab was discovered
during restoration works that contributed to re-date the stuccoworks to the second half of the
12th century. Finally, rejecting the current assumptions, which attribute the wall paintings
to the 14th century, it was proved that the wall paintings were the first decorations of the
tomb created prior to the second half of the 12th century. The current work contains also a
corrigendum to our previous study published on the decorations of the tomb.

The potential of laser cleaning for paintings as an alternative to traditional cleaning methods has been recognized, and studies using industrial laser equipment have shown some potential. Irradiation at a wavelength of 248 nm has shown to be the most promising for natural resin varnish and overpaint removal, because it is strongly absorbed by triterpenoid varnish functional groups and associated degradation products (Georgiou 1998). However, it has been suggested that a minimal varnish thickness should remain intact to prevent any radiation from being absorbed by the underlying layers. This is because some painting materials have also shown sensitivity to laser radiation (Bordalo 2006). Research into the mechanisms of alterations which may occur due to laser radiation on resins, pigments and oils and its long-term effects has been scarce, and dispersed in its approach because of the multitude of different materials present in the paint layers (Chappé 2003, Sobott 2003, Melessanaki 2006). Thus, the systematic study of laser radiation interaction with paint materials is still important. The aim of this study was to advance the understanding of the effects that KrF excimer laser irradiation has on pigmented oil paint layers.