Scientific–technical study
ANALYSIS OF THE ARTISTIC PROGRESS AND THE STATE OF CONSERVATION OF THE WORKS
Picasso’s successive interventions in his works constitute a source of information of huge potential. The permanent collection is the backbone of a museum,[1] its raison d’être, which is why we have endeavoured to document the Museu Picasso collection as objectively as possible, studying the surface materials as well as those used in deeper layers. In order to embrace as many aspects as possible, several techniques of examination are applied, some of them complementary: overall analyses provide general information about the underlying image or images, enabling us to distinguish between different materials (original, added and even sometimes resulting from changes in ingredients) although not their chemical composition, which is obtained from specific analyses that also establish the nature of the materials.
A meticulous visual study of the painting under different sources of light is carried out in order to define the details of its superficial structure. This helps us establish the technique used in the application of colour, its state of conservation and the existence of possible hidden layers.
Infrared reflectography (fig. 15, p. 48) allows us to penetrate the underlying layers to reveal the differences in absorption of infrared radiation according to the characteristics of each material, the permeability of pigments and the density and thickness of the layers of paint.
Several partial images of Barcelona Rooftops were taken, enabling us to construct the complete representation at two frequency intervals of nearinfrared NIR2 (950–1150 nm) and NIR3 (1200–1550 nm). [2] The study was complemented by images of details, taken at NIRi (750–950 nm) frequencies and visible ultraviolet fluorescence.
The behaviour of the materials forming the works varies according to the electromagnetic spectrum frequency. The interaction of the radiation on matter can change considerably during these intervals, which is why the same image can reveal different information about the work.
Radiography also penetrates underlying layers in order to obtain images of varying intensity, according to the absorption capacity of materials. In the case of Barcelona Rooftops, a composition of four images was taken: distance: 2 m, kV: 15, mA: 6, exposure: 3.2 min.[3]
The purpose of this study is to determine the structure and composition of the innermost layers of the painting, as well as to establish the nature of the pigments and thickener employed by the artist. This examination also helps us identify the pictorial technique and the deterioration suffered by the materials.
Pages 48 and 49
THE UNDERLYING LAYER OF BARCELONA ROOFTOPS
1, 2, 3 and 4 details of the visible image
a, b, c and d details of the reflectography at frequency interval of near-infrared NIR3
fig. 15 Infrared reflectography study of Barcelona Rooftops
[1] Hans Ulrich Obrist, ‘Conversation with Pontus Hultén’, A Brief History of Curating. Zurich, JRP / Ringier, 2008.
[2] Images obtained through infrared reflectography: Department of Analytical Chemistry, Faculty of Chemistry, Universitat de Barcelona (José F. García, Clarimma Sessa, Àngels Miquel and Eva Marín).
[3] X-rays: SGS Barcelona
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Summary