Page 423 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

vary the initial pH values to between 6 and 7. Almost immediately an emerald green precipitate
formed, and this was filtered and dried several days later. Posnjakite appeared as lamellar, pale
blue, rhombic and twinned crystals, while malachite formed in the usual spherulites.
The same copper sulfate solution was used to make atacamite, and from ι to 7 g of sodium
chloride was added to the solution. Atacamite precipitation occurred at about pH 8. This initial
pH value was reached by adding the appropriate amount of ο.ι M sodium hydroxide.
To coprecipitate atacamite and malachite, ι g of sodium chloride was introduced in powder
form into the copper sulfate solution with stirring. By adding ο.ι M sodium hydroxide, the pH
was raised to 8, and then sodium bicarbonate was poured in (the authors fail to give quantities
or molar concentrations several times throughout these recipes). The atacamite and malachite
were then filtered off.

RECIPE 7 P E L I G O T B L U E
To make Peligot blue pigment, 250 ml of a 0.5 M solution of copper sulfate was placed in a 500 ml
beaker and stirred while adding 3 ml of a 30% ammonium hydroxide solution, which formed a
white precipitate. Then 10 ml of a 1 molar solution of potassium carbonate was added, drop by
drop. After 24 hours, a light blue precipitate developed that was filtered, washed, and dried
under reduced pressure. This yielded 2.48 g of a light blue powder. Debye-Scherrer powder
X-ray diffraction showed that the preparation was a mixture of two phases: brochantite
(ICDD 13-398) and copper sulfate hydroxide hydrate (ICDD 20-0357).

RECIPE 8 V E R D I G R I S C O M P O U N D A
In the replication of compound A, [Cu(CH 3 COO) 2 ] 2 -Cu(OH) 2 -5H 2 , using the method from
Gauthier (i958), 200 ml of water was placed in an 800 ml beaker and stirred vigorously while
29.61 g of neutral verdigris was added at 20 °C. This solution is close to saturation. It was heated
to around 90 °C and stirred while 6 M ammonium hydroxide was added drop by drop until a
fine product began to precipitate from the clear blue solution. The solution was filtered imme­
diately and allowed to cool slowly at 20 °C for 10 hours, after which the solution precipitated
blue-white needles on the side of the beaker. This product was labeled I . Crystallization also
A
occurred on the bottom of the beaker, forming irregular crystals of a deep blue color. This prod­
uct was labeled A3. The precipitated blue-white needles were collected, suction-filtered off, and
then added to an equal volume of pure ethanol. After vigorous shaking, the mixture was allowed
to setde for 12 hours and was then filtered and dried. This product was labeled A2.
Using a method derived from Rahn-Koltermann and coworkers (i99i), compound A was
1
replicated as follows: In a 1 beaker, a 11.7% solution of neutral copper acetate monohydrate
was made in 750 ml of water. While the solution was gently stirred and heated, a stoichiometric
amount of 23.6 ml of a 24% ammonia solution was added drop by drop within 8 minutes.

A P P E N D I X Β
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