Historical Painting Techniques, Materials, and Studio Practice

products in the dried oil film (19). These short-chain scission products, by
giving the structure a swollen matrix, confer flexibility to the oil film. Earth
pigments are then particularly suitable as grounds on flexible supports. To
speed the drying process of these grounds, artists advocated the use of prepolymerized
oil (20).
Most of the inorganic components of these colored grounds are hygroscopic
and are not easily wetted by organic media. Free fa tty acids in the oil would
act as surface active agents, and therefore an unpolymerized oil would be
preferable to ensure wetting of the particles and pigment aggregates.
Groen and Burnstock have fo und air pockets with earth pigments bound in
unpolymerized linseed oil (21, 22). This problem can only be aggravated by
the use of an oil with a reduced proportion of free fatty acids (23). The
presence of air pockets makes the ground porous, causing the paint layers
above to "sink in" as the paint medium is drawn down into the absorbent
ground.
Speedy drying achieved by applying the ground as an emulsion, as advocated
in Pierre Lebrun's Treatise, would also result in a porous film because of the
voids formed during evaporation of the aqueous phase (24). The absorbency
of the ground would be particularly problematic with artists such as Guercino
who, in his first phase, painted aUa prima, using the dark ground fo r his
shadows and often applying only one layer of paint. Malvasia, describing
Guercino's technique before the artist left fo r Rome, says that Guercino had
"an extraordinary speed of execution, in one go laying-in (bozzando) and
finishing" (25). In the case of Guercino, the complaints came from his clients
who felt that since they paid Guercino by the figure, they wanted to see the
whole figure, not one in which more than half was drowned in shadow.
Lanfranco and later Giordano were also known for their speed of execution.
This speed was castigated by most art theorists, because it was seen as pratica,
simple manual facility rather than the fruit of matured intellectual thought
and skill.
Exposed or thinly covered porous grounds would pose a problem when it
came to varnishing (for the restorer as well as the artist), but grounds suffering
from what the French call lithargeage present a similar problem in appearance.
The coarsely ground lead white would present a less absorbent ground, but
the rough granular surface scatters light, obscuring detail in the worst cases
and flattening the composition. Many seventeenth-century paintings suffer
from this problem (26).
Viewing distance and lighting
It is clear that in a painting such as Guido Reni's Abduction of Helen (Louvre),
which does not depend on the warmth of its shadows for the depiction of
depth and its illusion of space but rather on what Leonardo termed aerial
perspective and the diminution of colors, the impact oflithargeage is minimal,
and saturation of the picture surface not essential.
This is the case with paintings of what I have termed the "high finish" school;
that is, those by painters who did not paint alIa prima, nor availed themselves
in the Venetian manner of the artifice of large areas of shadow and light, but
rather achieved the illusion of space through "the diminution of the hues, as
much through their quality as through their strength" (27).
The relative importance of saturation in paintings that rely on their dark
ground for illusion of space was especially visible in a recent exhibition of
Neapolitan painting in Bordeaux. Two paintings by Caravaggio were hung
next to each other. One was a privately owned Doubting Thomas, with a high
gloss varnish, and the other painting was a Salome with the Head of St. John
the Baptist (National Gallery, London), which had a much more matte appearance
(28).
16
Historical Painting Techniques, Materials, and Studio Practice