Historical Painting Techniques, Materials, and Studio Practice

elonged to William Mallord Turner (Fig. 4) . It contained seventeen bladders
of solidified oil paint, all of which had been opened and sealed with a tack.
Each was labeled in German or English. Two were named as Gebr. Terra di
Verte and Gebr. Grune Erde, the term "Gebr." coming from the German
gebrannte for burnt or roasted (24).
EDXRF analysis of the paint on the surface of the bladders showed iron to
be the major constituent with traces of manganese and titanium. The Terra
di Verte contained a trace of calcium, the Griine Erde considerably more
with traces of potassium, rubidium, and strontium (frequently present in calcium
deposits). Green earth is a complex silicate colored by iron with a
structure similar to mica (25).
Dispersions of the two paints were made. The Gebr. Terra di Verte was a
rich orange-brown comparable to burnt sienna but more translucent. The
Gebr. Griine Erde was similar to raw sienna, but of a greener tone. This must
have been burned at a lower temperature, as a few green particles remained.
Under the microscope, the pigments were identical to green earth, with the
overlapping plates of the crystals visible on the larger particles. Calcite was
seen in both, but the Gebr. Griine Erde had, as indicated by EDXRF, a higher
proportion of it. The labels suggest that both bladders were prepared in Germany,
perhaps from two different sources of green earth.
The appearance of the samples brought to mind the unidentified brown pigment
seen by the author in several nineteenth-century landscape paintings,
usually mixed with Prussian blue, ochres, and so forth, to produce greens and
browns. It was suggested that it was the brown seen in the cross sections from
a painting by Constable then being examined. SEM-EDX analysis of the latter
at the National Gallery laboratory produced a spectrum identical to that for
green earth. It was later identified in several Constable paintings dating from
1811 to 1829 mixed in greens and browns (26, 27). Could Merrifield's "eminent
English artist" be John Constable?
The author has tentatively identified burnt green earth in paintings by Peter
de Wint and J. F. Millet (28).
Green earth was rarely used in England. The author has seen it only in
seventeenth- and eighteenth-century wall paintings (oil) and cartoons by Verrio,
Laguerre, Thornhill, and Robert Adam, all of whom trained in Italy or
France. Verona brown seems to have been adopted in the early nineteenth
century as a translucent addition to the earth and organic browns then available.
Verona was a source of one of the better green earths, but was abandoned
earlier this century (29).
By coincidence, Constable Project researcher Sarah Cove visited Brussels and
brought the author a bottle of pigment, Griine Erde Gebr., from an artists'
suppliers. This modern sample is a darker, duller brown; perhaps burned at a
higher temperature than the earlier examples, it too contains calcite.
Brown pigments tend to be neglected, partly, no doubt, because of the difficulty
in distinguishing the multitude of ochres, organic earths, and lakes.
Burnt terra verte has a quite distinctive appearance, is easily identifiable by
EDX, and may be more common than previously thought.
Smalt
The earliest blue glass colored with cobalt is from Eridu, Mesopotamia, circa
2000 B.C.E. Recipes survive from Ashurbanipal's library in Nineveh, circa
650 B.C.E. The Indians adopted Sumerian technology and were making cobalt
blue glass by the sixth century B.C.E. (30). The Egyptians were using
cobalt by circa 1400 B.C.E. The Romans were familiar with it; it was common
in Western Europe in the seventh century and occurs in the Sassanian and
Islamic periods (31).
The first appearance of smalt is in a wall painting (ca. 1000-1200 C.E.) in
Khara Khoto, Central Asia, and in the Church of Our Saviour of the Mon-
Darrah
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