Verdigris is a
green/
blue pigment used by painters throughout the
13th to 19th centuries. The
Old French/
Anglo French origin of the
word should come to no surprise, as France monopolized the manufacture
of the pigment for almost 700 years: "
verdigris" is derived from
vert-de-gris (green of grey) or vert-de-Grece (green of Greece). But as
Webster 1913 notes, the word is actually a corruption from the Latin
viride aeris (cf.
aerugo,
aeruginous).
The application of verdigris in ancient Greek and Roman culture is
well documented. Dioscorides describes a method of preparing verdigris
in his De Materia Medica (first century B.C.). Pliny noted
that aeruca can be scraped of natural copper ore, and Theophilus
describes several different types of verdigris, namely viride
hispanicum and viride salsum]. But the application of verdigris
is much older; around 2500 B.C., the Egyptians already used copper
compounds for various applications, and the material appears in the
records as early as 1500 B.C.
Ancient cultures of course had no knowledge of the chemical
composition of verdigris. All verdigris pigments consist of Copper
Acetate, Cu(CH3COO)2. The various green/blue
tones are obtained by small changes in the chemical environment, and
mainly the pH (acidity). Typical verdigris compositions are:
[Cu(CH3COO)2]2.Cu(OH)2.5H2O (blue)
Cu(CH3COO)2.Cu(OH)2.5H2O (blue)
Cu(CH3COO)2.[Cu(OH)2]2 (blue)
Cu(CH3COO)2.[Cu(OH)2]3.2H2O (green)
Verdigris was produced from Acetic Acid (vinegar) and copper.
Vinegar was of course available in sufficient quantities in the wine
producing regions of France, and this may explain their leading role
over many centuries. Remarkably, for nearly 700 years the entire
verdigris operation was controlled by women living in Montpellier.
These women had a monopoly on the production and sale of verdigis
throughout Europe; the recipe was a secret passed on from mother to
daughter until World War I.
The women of Montpellier used copper from Sweden to synthesize the
verdigris. First they rubbed copper strips with some verdigris (to form
seed crystals), and covered them with fermented grape
husks. After several days, crystals would form on the copper plates and
the plates would be transferred to dark sheds. They further corroded the
copper by dripping stale wine extract onto it, forming large spongy
verdigris crystals on the surface. The verdigris was scraped off,
dissolved in vinegar and recrystallized on wooden
sticks. The verdigris was then scraped off the sticks, crushed, and
sold.
As was already mentioned, verdigris was mainly used as a pigment.
The Greeks and Romans used it for paintings. The Dutch
masters mixed verdigris with oil to form green and blue pigments for
landscapes and drapery. Unfortunately, verdigris is not a very lasting
pigment; it easily blackens under influence of moisture,
alkalis, and interactions with other pigments such as lead
and orpiment.
Verdigris was also used to preserve woods, tint papers, and
illuminate stamps. The compound also had some medical applications;
disinfecting wounds, treating tinea, and to treat inflamed eyes and
cataracts.
References:
Chemical & Engineering News, American Chemical Society, January 7, 2002
http://www.sewanee.edu/chem/Chem&Art/Detail_Pages/Pigments/Verdigris
http://innovations.copper.org/0006/00-06-medicine-chest.html
http://www.labthink.com/paint.htm