Page 424 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

A cloudy green precipitate developed. This was decanted, centrifuged, washed, and centrifuged
again until a stable pH of 6.5 was reached. The product was dried over phosphorus pentoxide at
10.5 torr (1399.881 Pa). This yielded 17.68 g of a very fine green powder.

RECIPE 9 VERDIGRIS COMPOUND Β
A laboratory replication of Schweitzer and Mühlethaler's (i968) method of producing com­
5
pound B, [Cu(CH 3 COO) 2 ]Cu(OH) 2 · H 2 0, is as follows: In a beaker, 11.22 g of neutral verdigris
was dissolved in 150 ml of water with constant stirring. In a separate beaker, 1.12 g of sodium
hydroxide was dissolved in 20 ml of water; this solution was added to the verdigris solution with
constant stirring. A precipitate appeared, and the entire solution became soft and mushy. A stir­
ring bar was kept moving in the solution for 8 hours, but the precipitate did not redissolve. For
the next 4 hours, the solution was kept in a hood without any agitation and allowed to settle into
two layers. The top portion consisted of a gel-like blue material, and the lower portion appeared
a light cloudy blue. The cloudy solution was isolated with a Pasteur pipette and dried. A light
blue powder (sample BI) was obtained after evaporation under vacuum. The beaker with the
original gel was left for several days in air at 20 °C, and four different colored layers (B2, Β 3, Β 4,
Β5) appeared after the solution had dried. Starting with the uppermost layer and working down,
the following samples were obtained: a purple-colored solid (sample Β2); a dark blue-green
material (sample Β 3); a bright light blue material (sample Β 5); and a light green compound
(sample Β4). Sample Β4 proved to be an excellent match to a sample of medieval verdigris. All
compounds were powdered and dried in vacuum for 1 day.

RECIPE 10 VERDIGRIS COMPOUND C
Gauthier's (i958) method for preparing compound c, Cu(CH 3 COO) 2 [Cu(OH) 2 ] 2 , was repli­
cated as follows: In a 300 ml Erlenmeyer flask, 5.91 g of neutral verdigris was dissolved in 65 ml
of water. Cupric hydroxide was made by first dissolving copper sulfate in water and then adding
12 ml of 3 M sodium hydroxide. The precipitated cupric hydroxide was filtered, and 1.91 g of the
product was then added to the neutral verdigris solution with constant stirring. The flask was
heated to 65 °C and kept between 59 °C and 64 °C for 11 days. During heating, the color of the
solution changed to a light blue-green. The precipitate was filtered and washed with 3% neutral
verdigris solution (0.32 g/12 ml), 30 ml of pure methanol, and 30 ml of water before drying. The
precipitate was labeled C2.
Another method to produce compound c involved the following sequence: In a beaker,
11.22 g of neutral verdigris was dissolved in 150 ml of water with constant stirring. In a separate
beaker, 1.12 g of sodium hydroxide was dissolved in 20 ml of water. This was then added to the
verdigris solution with stirring, and eventually a fine deposit appeared that went back into solu­
tion. The solution was covered and left for 4 days, after which blue crystals started to form,

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