Historical Painting Techniques, Materials, and Studio Practice

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Figure 2. XRF spectrum of yellow area on belt of Adonis. High peaks fo r arsenic and sulphur suggest
the presence qf orpil11ent.
particles, being enclosed in the oily medium, would no longer be incompatible
with other pigments, as they were in the previously used tempera techniques.
The radiant brilliance of their color in this new medium may have
contributed to their popularity.
Ochres were used to paint the landscape, the brownish color of the dogs, and
the golden vase near Venus's seat. Yellow ochres (hydrous iron oxides) were
identified under the microscope by their optical properties and by the presence
of high peaks fo r iron in the XRF spectrum.
Blue pigments. The major blue pigment used on this painting was natural
ultramarine (Fig. 1). Samples taken from the deep blue of the mountain range
appear under the microscope as pale blue, splintery particles with a low refractive
index (n < 1.66). In the cross section, one can see a single layer of
densely packed blue particles.
XRF of several blue areas showed high peaks for cobalt, potassium, and arsenic,
strongly suggesting the presence of smalt, an artificial pigment made
from potassium-rich glass deeply pigmented with cobalt oxide and ground
to a powder. Gettens and Stout suggest that the earliest occurrence of cobaltcolored
glass in Europe may have been in the early fifteenth-century Venetian
glass industry (8) . As the colorant for the glass, a substance called zafran is
mentioned. A recipe in a fifteenth-century treatise already mentions the preparation
of smalt as a smalto cilestro (9).
The source of the smalt in the Getty painting may have been Saxony or
Bohemia, where sixteenth-century glassmakers used the locally mined cobaltite
(CoAsS) and smaltite (CoAs2) minerals, which contain large amounts
of arsenic, to make smalt. The high peaks of arsenic measured by XRF, in
combination with those of cobalt, seem to indicate that cobaltite or smaltite
minerals were the source for the blue pigment. It is unclear whether the
zafran, or zaffer of Italian descriptions, has the same composition as the northern
European cobaltite. In other areas of the painting's sky, the original ultramarine
was scumbled over with a pale, milky blue. Examination of cross
sections of those areas shows that the pale blue consists of a layer of almost
completely discolored glassy particles.
Red pigments. Vermilion appears in Adonis's red sleeve. Its presence was established
by discovering high mercury peaks with XRF and confirmed by
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Historical Painting Techniques, Materials, and Studio Practice