Historical Painting Techniques, Materials, and Studio Practice

strating that spreading this glaze thinly in several layers is not merely a matter
of style but also a technical necessity.
The green tablecloth in Jan Davidsz de Heem's Still Life with Fruit (Cambridge,
Fitzwilliam Museum), painted in 1650, consists of a green glaze over
a dark brown underlayer with yellow-green highlights. Clearly this green
glaze has been applied with a brush, as the fairly clumsy brush marks are
visible. Along the contours of the vine leaves and on either side of the thin
stalks of the cherries, the green glaze leaves a gap showing the dark brown
underlayer. It is quite clear that this glaze must have been a rather viscous
liquid and therefore difficult to paint out with any precision.
The recipes for making copper resinate, collected by the doctor Theodore
Turquet de Mayerne in London between 1620 and 1640, are generally considered
to be the earliest. They call for verdigris to be heated with Venetian
turpentine and oil of turpentine as follows: "Beautiful green: take 2 ounces
of Venetian turpentine, 1 112 ounce of oil of turpentine, mix and add 2
ounces of verdigris in little pieces. Set it on hot ashes and let it boil gently.
Try it on some glass to see if you like the colour; strain it through a cloth"
(14) .
Trying out the recipe, it was found that the verdigris did not dissolve in the
mixture of Venetian turpentine and oil of turpentine because there was not
enough resin present; also, the presence of oil of turpentine hampered the
reaction of the copper acetate with the Venetian turpentine. When more resin
in the fo rm of rosin was added, a dark green resinous substance resulted,
which was liquid while hot, but hard and glassy as it cooled. This green glassy
substance can be ground in oil like a pigment. When ground in oil, however,
the color is no longer very intense.
Another recipe in the De Mayerne manuscript asks for verdigris, ground in
oil, to which hot common varnish is added: "Painters, i.e. those who paint
as well as those who paint furniture and blinds, grind verdigris with linseed
oil and then add common varnish, stirring it well. They allow the impurities
to sink down and only use the clear liquid, which they apply warm" (15).
With the term "common varnish" a solution of resins in oil is meant. This
recipe was the base for the experiment described above, grinding verdigris
in oil and heating it.
The preparation and application of the green glaze is not the only secret of
de Heem's tablecloth: the dark reddish-brown undermodeling gives the green
glaze its velvety depth. This observation proved to be very useful during
retouching. The only way to match this intense dark green color was to
reconstruct the build-up of layers exactly. The verdigris in the green glaze
was substituted with the transparent green pigment viridian (because of its
stability) and a little synthetic Indian yellow to match the required tone.
The reason a green glaze over a reddish-brown underlayer appears so very
dark lies in the absorption of the waves of the spectrum: green absorbs all
red waves, red absorbs all green waves. The two layers superimposed absorb
practically the entire spectrum of visible light, so that the resulting color is
almost black.
The painter's use of green glazes and grisaille
The green curtain in Titian's Tarquin and Lucretia (Fitzwilliam Museum)
shows green glazes over an undermodeling in red with broad white highlights.
The idea is ingenious. To start with, Titian underpainted the curtain in gray
with some azurite, then he laid in the modeling with a brownish red containing
some red lake and some very generous white highlights. As he applied
the green glaze, the shadows in the folds appeared very dark green, the middle
tones were light green because of the green glaze over white brush strokes,
and the flickering highlights remained white from the undermodeling, partly
emphasized with an extra brush stroke. In some places, Titian allowed the
red to shine through, giving the material a wonderful shot-silk effect.
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