Colnaghi Foundation Journal 03 - Magazine - Page 167
164
Scientific intervention in two major Murillo canvases
Since the aim was to use the priming layers as a colour
base for the different areas of the picture, the tone of
this stratum changed according to the painter’s needs.
The thicknesses measured in the ground layer of both
pictures can be as much as 300 um and the priming layers
vary between 35 and 150 um. These are made up of two
wet layers which, added to the ground layer, constitute a
preparation of considerable thickness (fig. 4). The ground
and priming layers of these two canvases closely resemble
those analyzed in Christ Healing the Paralytic at the Pool of
Bethesda, one of the six oil paintings made to decorate
the nave of the church of the brotherhood of Santa
Caridad, now in the National Gallery, London (fig. 5).12
Similarly thick layers have been identified in other
Murillo paintings such as Saint Diego de Alcalá (Madrid,
Real Academia de Bellas Artes de San Fernando), The
Miracle of Saint Francis Solano and the Bull 13 and Saint
Francis where the binding agent used was linseed oil.
Fig. 4 / Cross-section of the
stratigraphic skin-tones
of the work Moses and the
Water from the Rock of Horeb.
Thickness of the rig (1a) and
primer (1b) and the distinct
layers of polychrome (2, 3, 4)
and lastly varnish.
This combination corresponds to that recommended in
contemporary treatises on painting technique, describing
the usual procedures for preparing canvases as followed
by the seventeenth-century School of Seville. Pacheco
and Palomino both recommend applying coloured
priming layers to obtain tones which can vary from
dark brownish-greys to reddish-browns using what were
called “Seville earths”, i.e. mud from the Guadalquivir,
to which were added calcite and lead white as siccative.
They also recommended re-using leftover pigments14 to
speed up the drying process, and this has been observed
in the priming layers under analysis.15
Scientific intervention in two major Murillo canvases
The non-invasive MA-XRF technique was applied to
the whole paint layer, showing the spatial distribution
of pigments over the surface in all the works analyzed.
High velocity data collection scans were carried
out (4,000 X-ray fluorescence spectra per second
and detailed measurements every millimetre). The
palette Murillo used was shown to contain a fairly
small number of pigments which the artist used with
consummate skill to achieve a very diverse chromatic
range (fig. 6).
Combining the results of these non-invasive
techniques with the stratigraphic studies gives a fuller
understanding of Murillo’s technique. The crosssection of the polychromy of the canvases reveals a
complex stratigraphic structure when compared with
the paintings of his early period.16 In the later period,
Murillo used more paint layers to achieve the effects of
softness characteristic of his “diaphanous style”.
Smalt and azurite have been identified in the blues
and, in The Miracle of the Loaves and Fishes, lapis lazuli as
well. Obviously, the choice of blue pigment for various
parts of the canvas was largely influenced by economic
considerations. This is clearly demonstrated in large
areas like cloudscapes, where the much less expensive
smalt was used; whereas on the clothing and other,
smaller areas, azurite, sometimes mixed with smalt, is
found. The most expensive pigment, lapis lazuli, was
reserved for the most important areas, such as Christ’s
cloak. A thick under-layer of smalt gave the colour
strength, and the lapis lazuli could be applied on top as
a thin wash, between approximately 6 and 24 um thick.
Both canvases show deterioration due to the use of
unstable pigments such as smalt, which tends to turn
brownish-grey, as can be observed in the clouds of
The Miracle of the Loaves and Fishes or the robes of one of
the figures in Moses and the Water from the Rock of Horeb
(see figs. 1 & 2). This change was probably due to the
painting’s exposure to very damp atmospheres, though
the smalt has not been affected in the light areas of the
clouds, where it is mixed with lead white, since, in the
opinion of some authors, this acts as a stabilizer in the
pigment.17
Most of the yellows used lead tin yellow, in some cases
mixed with ochres to darken them. The greens are
made of a mixture of azurite and lead tin yellow, with
additions of vermilion, red lake, and occasionally red
ochre, to obtain different shades.
Fig. 5 / Bartolomé Esteban
Murillo, Christ Healing
the Paralytic at the Pool of
Bethesda, 1667-1670, oil on
canvas, 237 x 261 cm, London,
National Gallery.
Fig. 6 / X-ray fluorescence
mapping.
165
