Page 428 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

were a dark blue film and a vivid blue granular precipitate. These were dried under reduced
pressure. The dark blue material was a close match to the data for compound A that were
obtained by van T'Hul-Ehrenreich and Hallebeek (1972). The vivid blue precipitate matched
either compound A or H, again with high d-spacings at 16 Â.

RECIPE 12 PLINY'S VERDIGRIS
To replicate Pliny's verdigris recipe from his Natural History (Pliny 1979:34.28), two mixtures
were made using a copper mortar and pestle: (1) potassium aluminium sulfate and sodium car­
bonate and (2) potassium aluminium sulfate and sodium chloride. Each mixture was ground
with enough distilled vinegar to make a paste. Over the next 5 days, more distilled vinegar was
added to the mixtures, which were ground with the pestle until a light green paste developed.
The paste made with sodium carbonate had dried to a pale blue powder that gave an X-ray dif­
fraction pattern matching chalconatronite. The mixture with sodium chloride gave atacamite.
This last recipe was repeated, yielding a light blue powder that possibly contained a basic verdi­
gris as well as atacamite.

RECIPE 13 THEOPHILUS'S "VIRIDE SALSUM"
Theophilus's recipe (35) for "viride salsum" was replicated using a box approximately 10 by 8 cm
hollowed out of a piece of oak. Copper strips with honey and salt were placed inside, spaced by
small twigs; 60 ml of warm wine vinegar was poured over them, and the box was sealed up for
4 weeks (28 days). The product appeared to be a mixture of two phases: a light blue product
identified as a basic copper acetate (compound B); and the principal product, shown by X-ray
diffraction to be the neutral copper acetate monohydrate.

RECIPE 14 CALCIUM COPPER ACETATE HEXAHYDRATE FROM THE MAPPAE CLAVICULA
In replicating recipe 3 from the Mappae clavicula, solutions (0.25 M) of calcium acetate and cop­
per acetate reagents were made up with distilled water. One hundred milliliters of each solution
was poured into two wide, open glass beakers and stirred. This resulted in a clear blue solution.
One beaker was placed in an oven at 40 °C, and the other was left in a fume hood to evaporate.
After 3 days, the oven solution had reduced in volume by 50%. Crystals, identified as calcium
acetate, had formed around the sides of the beaker above the solution, which was by then of a
viscous gel consistency. There were some crystals on the surface of the gel as well. The solution
in the fume hood was unchanged. The oven beaker was transferred to the fume hood as well, to
slow the evaporation. Two weeks from the start of the experiment, the contents of the oven
beaker were heterogeneous: a blue-and-white granular area; a dark blue gel; some blue-green
crystals; and a fine, light blue powdery area. The fume hood beaker contained a dark blue liq­
uid with some long, fibrous, light blue precipitate. One week later, the fume hood sample was
nearly dried and consisted of a light blue fibrous residue; blue-green grains (probably unreacted

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