Page 300 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

ticularly related to the Mappae clavicula tradition, it does contain the following closely related
recipe for a blue pigment:

[39] To make a beautiful blue at little cost. Take quicklime and green and ground verdigris
and sal ammoniac, as much of one as of the other. Grind these all together with urine and
you will see a beautiful blue. Temper it with the previously described glair [egg white],
when you want to work with it. (Wallert 1995:43)

i
The "green" referred to here is an organic sap green. As seen with recipe ii of the Mappae cla­
vicula, reactions with lime, or in this case with quicklime (calcium oxide), are likely to produce
complex or unusual salts, such as calcium copper acetate hexahydrate. Here the addition of
sal ammoniac (ammonium chloride) suggests that mixtures of the calcium copper acetates and
copper trihydroxychlorides are quite possible, since adding ammonium chloride tends to result
in the replacement of the acetate groups with basic chlorides. Combining copper (verdigris),
organic plant substances ( green), and urine components adds to the probable complexity of the
products of this particular recipe. This, in fact, proved to be the case: a laboratory synthesis of
the recipe from the Simone manuscript for a blue pigment produced soft turquoise particles that
did not give an identifiable powder X-ray diffraction pattern.
The following recipe from the Mappae clavicula is for "Byzantine Green":

[recipe 5] f you want to make Byzantine Green, take a new pot and put sheets of copper in
I
it then fill with very strong vinegar, cover and seal, leave for six months. The product can
be dried in the sun. (Smith and Hawthorne 1974:27)

Another set of instructions from the Mappae clavicula (recipe 10) mentions that Byzantine
green can be tempered with vinegar, which would convert the basic verdigris salts into neu­
tral verdigris (Smith and Hawthorne 1974:27). This would help produce a purer product on
recrystallization.
The Mappae clavicula also gives instructions for making "Rouen Green":

[recipe 6] Rouen Green. Take sheets of copper, smear with soap. Put the sheets into a
pot, fill with vinegar, cover, seal and place in a warm place for fifteen days. (Smith and
Hawthorne 1974:27)

APPENDIX B, RECIPE 15, describes the replication experiment for this recipe, which produced
a light blue material that is probably basic verdigris.
The following process from the Mappae clavicula calls for the use of copper strips:

[recipe 221-D] Take copper strips and scrape them down well and hang them over vinegar.
Scrape off and gather the stuff that collects on it. (Smith and Hawthorne 1974: 6i)

T H E ORGANI C SALT S O F C O P P E R
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