Historical Painting Techniques, Materials, and Studio Practice

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Figure 3. Fluorescence spectrul1'l of red lake pigment on shirt of Adonis. Quantum yields at A em 445
nl1'l to A ex 397 nm and A em 433 nl1'l to A ex 355 rim indicate preSe/1ce of a cochineal dyestuff.
microchemical tests and PLM of a sample taken from the area. The other
reds in Adonis's tunic and the clothing draped over Venus's seat were of an
organic nature. In a sample taken from the seat, an organic colorant was fo und
that also showed the presence of a few textile fibers. This led us to believe
that the red lake may very well have been a so-called lacca de cimatura de grana.
These cimatura lakes were made by an early recycling process. The dyestuffs
were precipitated into a pigment lake extracted from red textile clippings or
shearings (cimature) from a tailor's workshop. The making of such lakes was a
fairly common practice, and its description can be fo und in numerous fifteenth-
and fourteenth-century recipe texts (10). The procedure could be
performed with most of the available red textiles. The dyestuffs most likely
to be found in these lakes are anthraquinone-type dye, such as kermes, cochineal,
lac dye, and madder. The analyses by FS and TLC showed the presence
of more than one organic colorant; the red appeared to be a mixture. A sample
taken from Adonis's garment showed a good match with a library scan of the
cochineal standard (Fig. 3). The results were confirmed by chromatography,
which also indicated the presence of purpurin, a colorant present in madder
type dyestuffs. No spot for alizarin, the major coloring component of common
madder (Rubia tinctorum), could be found. Several possible conclusions
are indicated: (a) wild madder (Rubia peregrina) was used, (b) a specific technique
was used for the dyeing of the original textile, or (c) the alizarin was
not fully extracted in the cimatura process. This finding supports the suggestion
that the lake was a cimatura de grana-lake, and the painters who extracted
the dyestuffs from textile shearings had no control over the actual dyestuff
composition. Since they are similar in color, and not readily distinguishable,
any madder-dyed textiles could easily have been included in a larger batch
cochineal-dyed clippings.
Lake pigments are known to dry poorly. It was common practice, therefore,
to add ground glass to lakes. Sixteenth-century glass was typically very rich
in lead; the lead in the glass would act as a siccative, thus promoting the
drying of the paint. An interesting passage in the Paduan manuscript describes
the process: "To make lake indigo and lamp-black, dry quickly. Grind them
with oil, then take glass ground to a very fine powder, and incorporate with
the colors by grinding them together again; and thus, in the space of 24
hours, they will dry" (11).
Examination of a microsample of the red lake of Adonis's shirt did, indeed,
show the presence of small glass particles. The purplish red of Venus's seat,
on the other hand, was made of a mixture of an organic red lake and smalt
(Fig. 4). In this case, the smalt had a double function. It gave the carmine lake
a more purple color and at the same time acted as a siccative.
White pigments. The white pigment found on the painting was lead white.
XRF revealed the presence of lead in the sky and in the flesh tints. Polarized
Birkmaier, Wallert, and Rothe 123