Historical Painting Techniques, Materials, and Studio Practice

arrow in Adonis's right hand ends at the edge of the painting. The loss may
be estimated at 5-9 cm. On the basis of a comparison with the Delignon
print, the original size of the painting may have been 172 X 213 cm.
Ground
The painting has a conventional gesso ground. The ground was chemically
identified as calcium sulfate. XRD has shown that it consisted of a dihydrate
gypsum. This composition is common fo r Venetian painting at that time.
Gypsum of the dihydrate form occurs when it is used in its natural state. The
use of unburned gesso-as opposed to burned gesso, where crystallization
water is driven off to an anhydrite form-seems to occur primarily on Venetian
paintings. PLM examination, however, has shown that a considerable
amount of anhydrite particles were also present. Paintings from Florence and
Sienna more often show the presence of anhydrite or hemihydrite grounds
(5). Gesso grounds of this type were the same as those used for ground layers
on panel paintings, and its use stems from this tradition. In panel paintings,
however, several layers of gesso-gesso grosso and gesso sottile--were applied.
The brittleness of the gypsum layers, which form a good first ground on
panels, would cause it to crack off too easily from a canvas. Therefore, artists
began using thinner gesso layers on canvas; eventually, in the eighteenth century,
an oil priming was used instead.
The ground on the Getty Titian is rather thinly applied so that it only fills
the spaces between the warps and wefts of the canvas. Cross sections show
that it is an unpigmented ground. In some areas, an oily layer containing a
few charcoal-black particles was found between the white ground and the
first paint layer. It was only later, in the paintings by Tintoretto, for instance,
that a colored ground became more common. A passage in the Volpato
manuscript refers to Titian's use of white gesso grounds as opposed to the
increasing use of colored grounds by other, more modern Venetian painters.
Staining of microscopic cross sections with specific reagents gave strong indication
that the binding medium of the ground contains proteinaceous material;
this was confirmed by the presence of specific FTIR absorption bands.
Infrared mapping allowed us to locate the presence of specific bands in the
cross sections.
Underdrawing
Infrared reflectography revealed some evidence of underdrawing. The interpretation
of the infrared reflectograms is difficult, however, as some features
that showed up as broad, dark lines in the reflectogram could be carbon black
used in the paint, rather than the underdrawing. It is not immediately obvious,
for instance, whether the dog's curled tail in the original underdrawing was
intended to be straight. The broad, dark form in the reflectogram may represent
a dark, carbon-black pigment in the painted tail, which was actually
intended to be curled in the underdrawing. The reflectogram shows sketchy
lines in the trees in the background. The sleeping Cupid seems also to have
been rapidly sketched before painting. In all, no significant deviations from
the preparatory drawing appear to have been made.
Paint layers: the medium
Staining of cross sections indicated that the actual painting was executed in
an oil medium. This was confirmed by the presence of characteristic absorption
bands in the FTIR spectrum (Fig. 1). Three samples were selected for
examination with gas chromatography. One sample consisted Inainly of paint
fo r the golden vase in the painting's lower left corner. The other samples
contained blue particles for the sky. Contemporary sources often indicate the
use of walnut oil, which was generally considered to yellow less with age, for
the making of blue paints. Earlier studies of Titian's paintings have revealed
that the artist used both types of oil on different occasions. Chromatography
showed an azelaic:palmitic acid ratio in all three different samples, indicating
Birkmaier, Wallert, and Rothe 119