Page 425 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

and a fine white sediment settled out at the bottom of the beaker. The blue crystals were sepa­
rated from the solution and formed into two small cakes that were allowed to air dry. An efflo­
rescence of neutral verdigris formed on the outside of the cakes and was removed. It can take
as many as 14 days for the cakes to dry sufficiently. The cakes were then crushed, and the green-
blue crystals were washed and dried. This synthesis was not particularly successful because the
cakes were too small to produce a discrete surface efflorescence. A second synthesis was made
by dissolving 5.9 g of neutral verdigris in 65 ml of water in a 300 ml Erlenmeyer flask. Then 1.91 g
of freshly precipitated cupric hydroxide was stirred into the solution, and the flask was covered
°
and maintained at a temperature between 60 C and 63 C. The chemical changes were followed
°
by observing the color changes of the salt. The sediment was agitated occasionally. The reaction
took from 8 to 10 days to go to completion. The precipitate was washed first with a 3% neutral
verdigris solution and then with water and alcohol and dried at 30 °C.
In the preparation by Rahn-Koltermann and coworkers (i99i), 100 g of neutral copper
acetate monohydrate (0.5 mol) was dissolved in 750 g of water. The solution was stirred vigor­
ously and heated just until the boiling point was reached. After the solution cooled, 3 ml of a 24%
ammonia solution was added drop by drop until a light green precipitate developed. This was
filtered and then dried for 2 days under phosphorus pentoxide and a reduced pressure of 10 torr
(1333.22 Pa).
°
The filtrate was next placed in a beaker under ethylene glycol at 40 C. After 48-64 hours,
a cloudy light blue precipitate appeared. The solution was decanted, and the residue centrifuged
for 10 minutes, washed with water, and centrifuged again until a stable pH of 6.5 was reached.
This step had to be done rapidly; otherwise the layered product would turn brown between
solid and liquid phase after 15 minutes of standing. The products were dried in the usual way
and produced 1.39 g of light blue product and 3.75 g of light green precipitate.

RECIPE 11 VERDIGRIS COMPOUND D
A laboratory experiment to replicate Schweitzer and Mühlethaler's (i968) method of making
compound D, U ( C H 3 C O O ) 2 [ C U ( O H ) 2 ] 3 - 2 H 2 0 , is as follows: In a 31 beaker, 2000 ml of water
C
was stirred while 127.7 g of neutral verdigris was added. The solution was then divided into two
equal portions. To one portion, concentrated NH 3 solution was added drop by drop while stir­
ring. After about 13 ml of the N H 3 had been added, a sediment formed that, when about 30 ml
of the N H 3 solution had been added, was highly viscous; further additions dissolved it again.
When about 80 ml of the N H 3 had been added, everything was in solution again. While this
solution was vigorously stirred, the second portion of neutral verdigris was added. This homog­
enized the precipitating gel-like sediment. The mixture was left to stand, and after about 4 to
5 days, beautiful deep green crystals formed at the bottom of the beaker. The solution above
them was clear. The crystals were washed with water and alcohol.

A P P E N D I X Β
408