wood panel
Artists of the Italian Renaissance, during the 15th and early 16th centuries, usually painted on thick panels of poplar wood composed of several boards that were glued together. Wooden dowels were sometimes used to reinforce the joins, and then the panel was planed smooth by specialist carpenters or woodcarvers. Mainardi used a large panel made of 6 boards to create this altarpiece. The wood is poplar, a light heartwood—wood from the center of the trunk—with vertical grain. The panel may originally have had wooden battens nailed to the back to provide extra strength for the boards.
gesso
The artist or his workshop assistants prepared the panel for painting by first sizing the raw wood with a thin animal glue solution to make it less absorbent.
Flaws in the panel, such as knots, and the joins were covered with thin patches of a gauzy fabric attached with glue before a thick ground was applied by. brushing on many layers of a white gesso made from gypsum (calcium sulfate) and animal glue. Mainardi used the traditional method of first applying coarse layers of gesso grosso (the anhydrite form of calcium sulfate, made by heating it in a kiln), followed by an application of smooth and fine gesso sotile. The calcium sulfate is slaked, or soaked in water until it is “as soft as silk,” in the words of Renaissance painter, Cennino Cennini. A thin sizing of oil and/or resin may have been applied to reduce the absorbency of the gesso prior to painting.
design
A pattern was probably used to transfer the design for the painting, since the contours of the figures, the drapery, the architecture and the haloes were deeply incised into the gesso with sharp tools. A very similar version of this painting is in Incisa Valdarno, outside of Florence, Italy, which lends support to this hypothesis.
Incising the contours provided a guide for the artist and/or his assistants, who could then draw in details to further aid the painting and gilding process. The inner perimeter of the painted border is also incised, suggesting that it is original to the composition.
paint
The paint appears to be a traditional egg tempera medium (dry pigments mixed with egg yolk) applied in a manner more typical of the mid-15th century than early 16th century, when many artists were beginning to use colors ground in oil or a mixed technique that employed both tempera and oil media. It is possible that Mainardi painted some final touches in an oil or oil/resin medium, but this has not been confirmed with scientific analysis.
A greenish verdaccio underpainting is used below the flesh tones and is reminiscent of an earlier technique. The paint is applied in layers with delicate cross-hatched and parallel brushstrokes in the three values (dark: pure pigment; middle: some white added; and light: more white added) to create modeled form and volume.
Burnished gold leaf attached with a water-based adhesive was used for the haloes and other decorative elements (although the traditional red clay, or bole, layer does not seem to be present), and mordant gilding (gold leaf laid over delicately painted lines of a sticky drying oil) was used for the brocade designs on top of the tempera paint.
To learn more about Italian Renaissance painting materials and technique, click here.