The degree to which the durability of a painting was thought to rely on
the preparation is evident in a contract of 1585: “Firstly, it is a condition
that the altarpiece and the tabernacle [custodia] ar e to be prepared accord-
ing the the custom of the master painters in such a way that it fails not,
but rather will survive in perpetuity, and otherwise [the painter] must
make it again at his own expense if there should be any damage arising
from fault in the preparation” (García Chico 1946:153).
The application of glue-based preparation layers to the panels was
a complicated affair and one on which importance was placed not only in
the contracts but also in the ordenanzas de pintores(civic regulations gov-
erning trade), if we are to judge by the example of the ordenanzas from
Cordova already mentioned. Much attention to the isolation of knots
and the resin they could produce is evident in contracts and even merits
detailed commentary from Pacheco: “Pine is the wood ordinarily used for
architecture and sculpture. It tends to weep resin, particularly from its
knots, which are very large. At times, the resin even penetrates the prepa-
ration. Experience has taught that the best remedy to avoid this danger is
to cover the knots with pieces of linen and very strong paste-glue [engrudo]
after applying the glue with garlic [gíscola] and to make the preparation
over this as it is not enough to have punctured, burned out, and gone over
the knots with garlic” (Véliz 1987:86). Attempts to prevent such staining
indicate that the white pine, free of knots and so prized in Castile, cannot
always have been available, since painters sometimes had to deal with
knots in this way.
One or several layers of parchment size or other fine glue size
were applied over the wood. Contracts and guild regulations suggest that
mastery was needed to achieve the successful tempering of the glue mix-
tures, but since both strong and weak glues are recommended in various
documents, it is best to agree with Pacheco that some masters preferred
a strong glue, others a weak one. He tells us, though, that whatever its
strength, the glue had to be applied very hot (Véliz 1987:86–87). The
first glue layer applied to the wood was frequently prepared with garlic
(gíscola). The precise purpose of this additive is undocumented, although
it is possible to hypothesize that it served not only to lower surface tension
but also to act as a fungicide.
After the first glue priming, the linen or hemp cloth or fibers
would be applied and then soaked with stronger glue. Although these
were the most common materials, parchment (used in conjunction with
hemp fibers) is named in a contract dated 1477 (Sobré 1989:53). The panel
would then be ready for the preparation layers.
Gessoes were formulated in Spain, as they were elsewhere, with
either calcium carbonate or calcium sulphate, depending on the region;
calcium carbonate was more common in Castile, calcium sulphate more
common in Valencia and Andalusia (Sobré 1989:53). The most detailed
account of the application of gesso layers comes from Pacheco, whose
comments generally reflect local practice, although his writing is clearly
informed by such sources as Cennino Cennini (author of the fifteenth-
centuryIl libro dell’arte) (Cennini 1954). He tells us that “the first layer of
gesso [yeso grueso] should be applied hot, not too thick... up to four or
five layers (but never more than these)... the yeso mate should be applied
with the same glue as the yeso grueso... I say it can be the same as the
grueso because the thinness of the yeso mate moderates the strength of
the glue” (Véliz 1987:66). A further warning is given when he says, “SomePreparation Layers
142 Véliz