Description of the pictorial technique through stratigraphic study
From the interphases[1] of the stratigraphic cuts we infer that when Picasso made Barcelona Rooftops, the underlying layer, i.e. the one on which we discover the couple, was already completely dry, thus confirming the fact that a fair amount of time elapsed between the two exercises. At some point before he began the latter composition he removed some of the fresh paint with a spatula so as to be able to work smoothly and prevent the colours from merging. We are unable to say whether the surplus paint belonged to the composition of the couple or to another discarded attempted that bore no relation to the other two compositions.
Barcelona Rooftops must have been painted relatively quickly, for Picasso used much white lead applied in very thin and free-flowing layers of colour. The presence of this pigment and of thinner for diluting his colours would have helped hasten the drying process. To complete the painting Picasso applied at least three layers, starting from the darkest shade and superimposing pale tones. The purest blue was used exclusively for drawing the main lines of the buildings, while pure white was reserved for the clouds.
Four micro-samples (< 1 mm2) of sufficiently representative areas were taken to prepare the stratigraphic analyses, taking advantage of the fissures in the layer of paint. The two outstanding characteristics of these samples are summed up in colourful complex strata in the inner layers, due to the fact that the painting was executed in different stages and with noticeable changes in colour. This forms a sharp contrast with the final visible effect – a scene dominated by blue, enhanced by touches of earthy colours – and proves that Picasso transformed his palette in a limited space of time. Certain changes in technique and the gradual loss of matter in favour of thinner and more free-flowing layers of colour can also be appreciated.
The area that contains the couple conceals very bright colours that are visible in the stratigraphic studies, and even at first glance, through the fissures in the paint. The rosy flesh tones are achieved with pink and brown silhouetted in blue, while the orangey pink surrounding ground seems to cover large planes, although it has not been rendered in Pointillist or fragmented brushstrokes.[2]
Thanks to the images obtained by molecular spectroscopy, X-rays, infrared reflectometry and visible ultraviolet fluorescence, and to the results procured by the analyses of sections of colour strata from the micro-samples we have an objective view of the two compositions in the work, Barcelona Rooftops and the nude couple, between which we have discovered traces of what could possibly be another composition in a third layer that has not been independently established.
[1] The space between the layers of paint that is visible only through a microscope.
[2] A technique employed by the artist from spring 1900 onwards that allowed him to cover large surfaces quite quickly thanks to the application of pure colours. As there is no physical merging, the eye combines the colours.
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Summary