The painting through a bull's-eye


Guardando il dipinto da un oblò (ITA)

Ritratto  di Giovanna Tornabuoni del Ghirlandaio  (1488, Museo Thyssen-Bornemisza, Madrid).

This nice detail of the girl wisely painted by Ghirlandaio helps us knowing better how a painting is made. We can imagine to cut a small slice of this painting, perpendicularly, just on one of the girl’s hands. Now we have a cross-section, exactly the one in the bull's-eye!. If we now observe this section with a microscope, we could distinguish different layers:
1.      ground,
2.      preparatory drawing,
3.      base for carnations,
4.      different layers of colours (from 4 to 6),
7.      varnish.

The ground is a layer directly on the painting support, i.e. the panel or the canvas, to make it suitable and stable before the pigment is applied. It is usually white, or with specific hues when transparencies and contrasts are required by the artist. It shouldn’t be so porous, thus to absorb excessively the binder. The atelier transmits the recipes for its preparation, but mostly it is composed by gypsum and glue for panels, with an addition of oil for a proper flexibility on canvas, and it can be applied in more than one layer. In the latter case, the last one has the name of “imprimitura”. It is a colourless and translucent layer made of animal glue, resin diluted in an organic solvent and eventually oil. It as the purpose of isolating the painted layer from the ground, reducing gypsum porosity and making the brush stroke more fluent.

On this ground the artist can reproduce a preparatory drawing, basically a draft, more or less detailed, of the subject to be represented, in more or less detail. This helpful drawing can be done with metalpoints (leaving a negative fingerprint on the surface), ink or charcoal. Otherwise, quadrettatura or cartone could be also used [1].

Now the painter can choose a hue for the whole preparatory layer. For example, if carnations predominate, the painter can attribute a pale green, usually made of the mineral glauconite, to the surface.

This is the moment for the pigments to be used, as previously prepared by the atelier. The pigment is applied in fine layers with a binder (transparent medium). Some layers may also be overlapped, as in the picture I chose for you. This is especially the case when the painter is not satisfied of initial hue and tries to change it with consecutive brush strokes and colours.

Finally, when the whole scene is painted, a final layer – or more than one - of varnish has to be applied. The purpose is the protection of the painted surface but also a greater aesthetic output. With the varnish, the surface becomes homogeneous: irregularities due to pigment grains (the red dots in our bull’s-eye) are flattened. The painting now appears bright and in high-contrast.

            After this curious “apnoea”…I invite you to have a look to the very well-built website of the ThyssenMuseum, where the painting in the bull’s-eye is hosted. There you can find an interesting overview of the diagnostic techniques used to know Ghirlandaio’s damsel better.

[1] Cartone means “cardboard”. The subject is reproduced on it and the contours are marked with a metalpoint. If this cardboard is then superimposed to the ground leaves markers. On the contrary, when a punch is used to trace the outline, the holes in the cardboard give a dotted figure on the ground layer if carbon black is plugged on it. The latter technique is the so-called “spolvero”.


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