Page 156 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

crystals; this suggests a synthetic preparation rather than natural mineral botallackite. The
complete folio page from which the sample was taken is reproduced in PLATE 32. PLATE 33
shows paratacamite from a nineteenth-century Japanese painting in the Freer Gallery of Art
(Fitzhugh 1988). The pigment particles are rounded, boulderlike crystals with variable green
transmittance in bright-field illumination.

OTHER B A S I C C O P P E R C H L O R I D E S

Connellite Connellite, Cu 1 9 (OH) 3 2 Cl 1 4 S0 4 -3H 2 0, was reported by Otto
(1963) to have been found on bronze rings from graves dating
to the La Tène culture (mid-fifth century B.C.E.) in southwestern Germany. The bright
blue, needlelike crystals were mixed with other copper minerals in the corrosion crust. As
a mineral species, connellite was identified from deposits in St. Daly, Cornwall, England.
The only other identification of connellite is from the work of MacLeod (1991) on Austra-
lian shipwreck sites. On a set of nickel-silver spurs from the wreck of the Macedón (1883), con-
nellite was found in association with the unusual zinc-substituted paratacamite, formally
known as anarakite and whose nomenclature was discussed earlier. These minerals were
found together with the nickel salt nickel hydroxychloride, NiOH · Cl, and a basic zinc sulfate,
ZnS0 4 3Zn(OH) 2 -4H 2 0.
Pollard, Thomas, and Williams (1990a) established that when even small amounts of sul-
fate ions are present in aqueous solution with chloride ions, the copper trihydroxychlorides can
be replaced by other insoluble mineral species, such as brochantite, Cu 4 S0 4 (OH) 6 , and con-
nellite. Thomas (1990) found that an unexpected blue crystalline material was produced
during attempts to synthesize the copper trihydroxychlorides, and this material was iden-
tified as connellite. There appears to be a solid-solution series between connellite and butt-
genbachite, Cu 1 8 (N0 3 ) 2 (OH)3 2 Cl 3 -H 2 0. Analyses of buttgenbachite show that the material
can exist without sulfate in the lattice (Schoep 1925), although other work suggests that there
is a considerable variation in the amount of sulfate and nitrate present (Palache, Berman,
and Frondel 1951). End member connellite with no nitrate is known. In the relationship between
connellite and buttgenbachite, it is not immediately obvious how two nitrate ions can sub-
stitute for one sulfate ion. The structure of the connellite crystal, however, is composed of
a three-dimensional network of C u , O H , and CP ions that contains large channels paral-
2 +
-
lel to the c axis. This creates a zeolitic-type framework where sulfate, nitrate, and water mole-
cules occupy the channels. The sample analyzed by Thomas (1990) has the complex formula of
Cu3 6 . 8 [(SO 4 ) 0 . 8 (NO 3 ) 0 . 2 ] 2 Cl 6 (OH) 60 {Cl 0 .33[OH 0 .33(H 2 O)] 0 .33}.6H 2 O.
Reexamination of the connellite originally described by Thomas showed that it is, in fact,
carbonatian connellite, a new variety of the mineral. The connellite was prepared by reacting
a solution of cupric chloride with sodium chloride and sodium sulfate. At first, the transient

C H L O R I D E S AN D BASI C C H L O R I D E S
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