Page 138 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Notes
ι Pliny the Elder Natural History 33.57 (Pliny 1979). 13 It is also quite possible that some of the artifi­
2 Pedanius Dioscorides De materia medica 5.17 cial pigments produced from early recipes are
(Dioscorides [1933] 1968). not, in fact, azurite, but other synthetic prod­
3 Pliny 37.19. ucts; this would explain the low refractive index
4 Ajournai published by the Getty Conservation found by Laurie.
Institute in association with the International 14 In medieval and Renaissance times, "mountain
Institute for Conservation of Historic and Artistic blue" was a synonym for azurite. As supplies
Works, London. of the natural mineral dwindled, this name was
5 Values of the isotopic ratios in carbonates are later applied to the type of synthetic preparation
expressed in deviations, in parts per thousand, described here.
from standard physical data, where delta = 15 If potash really had been used, however, the pre­
[(#sample/#standard) ~ l] X I n this equation, cipitate would actually have been the copper (II)
R is either the ratio of C/ C or 0 / 0 . hydroxide.
1 2
1 8
1 3
1 6
6 Evidence of other early uses of azurite has been 16 The first laboratory synthesis of the compound
found as well. Beads made of azurite, turquoise, to make use of this method was by Jean Achille
and a variety of other minerals were found at the Deville (1789-1875) in 1852 (Mellor 1928).
ancient Mesopotamian site of Yarim Tepe, dating 17 Silver overlaid with a thin coating of gold.
from the sixth millennium B . C . E . (Moorey 1994).
Carved azurite has also been found in the form of
two early cylinder seals from ancient Babylonia.
7 Pacheco was father-in-law of the Spanish painter
Diego Velazquez (1599-I660) .
8 Mayan blue is the most important synthetic
blue pigment invented in ancient South America
and consists of indigo absorbed into a good qual­
ity clay. The combination of the dye and clay
proved to be remarkably resistant to fading and
deterioration.
9 Andrew Watling, conversation with the author,
Los Angeles, 14 March 1998.
10 There is uncertainty about the characterization
of the basic chloride alteration products of azurite
because Fourier transform infrared spectroscopy
is not sufficiently precise to differentiate among
the many possible end products.
11 A very slight weight change observed at this tem­
perature may be due to loss of some bound water
or slight deterioration, so it is not clear at this
temperature that decomposition has yet occurred.
12 Understanding the heat alteration of malachite
also provides practical insight into the process
of reaction soldering. In this metallurgical join­
ing technique, gold granules are adhered to a sub­
strate metal (also usually gold) using malachite
and an organic-glue binder. On heating, the mala­
chite decomposes, loses water, and by 00 °C,
6
transforms into tenorite. The carbonized glue acts
as a reducing agent that then transforms the ten­
orite into copper metal, which diffuses into both
the gold granules and the gold substrate, creating
a metallurgical join. This soldering technique is
also known as "reaction hard soldering," or the
"Littledale process," because it was rediscovered
by the English jeweler Littledale in the 1920s.

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