Programme start: 2006

CICRP: Christine Benoit

Coloured layers, most often red or brown, have been used in the 17th and 18th to prepare the canvases of Western easel paintings. These preparation layers consist of iron oxides, ochres or earths, used with an oil binder, alone or in combination with other extenders.

Stratigraphy

Stratigraphy of a painting and its pictorial layers.

La chartreuse de Marseille, anonymous 18th-century work,

La Grande Chartreuse collection, Correrie Museum.

The study of the chemical composition of these preparations has several implications in the domain of conservation and restoration. Certain coloured preparations react to aqueous treatments, as a result of the presence of swelling clays in the pigment used.

Ochres are substances of essentially local provenance; determining their stratigraphic origin provides information on the location of the painting’s creation. The study of applications and their variations can contribute towards establishing schooling practices and serve as a chronological marker in the career of an artist.

Several lines of investigation have been explored: the development of identification protocols for the ochre constituents, particularly the clays and the swelling clays; the collection and analysis of ochres and natural earths of known provenance that can serve as a reliable reference for the study of ancient samples of unknown provenance; and the analysis of samples from ancient paintings bearing coloured preparations.

Coloured preparations

Coloured preparations of Provence. Michel Serre, L’apothéose de saint Roch [The Apotheosis of Saint Roch], Church of Mazargues

The collection and analysis of samples is carried out systematically on paintings restored by the CICRP to obtain statistically significant results.


Programme start: 2012

CICRP: Christine Benoit (director, pictorial materials), Emilie Hubert (imaging)

This programme concerns reverse glass painting or painting fixed under glass, with several perspectives: The study of technological aspects, on the one hand, since the techniques used have not always been well identified (for example, the possible ‘tack coats’ serving as interfaces between the glass and the painting). Tackling this question involves the study of different historical formulas and applications. On the other hand, the programme addresses specific issues of heritage collections particularly in relation to their restoration. In 2012, around 60 pieces from the Borély Museum were restored by the CICRP. Previous restorations (the evidence of which must be researched) carried out on a certain number of the collection’s pieces need to be identified as they pose a problem for the restoration efforts. The chronology and nature of these previous treatments on the collection, as well as the origin of certain pieces, must be clarified. A third angle consists of developing and finalising the scientific imaging for these works, so far little studied in heritage laboratories.

Assomption de la Vierge [Assumption of the Virgin Mary]

Assomption de la Vierge [Assumption of the Virgin Mary] medallion, 17th-century anonymous Italian work, Borély Museum. Front and reverse photographs before treatment. The deterioration of the silver foil is studied under stratigraphic section with a scanning electron microscope


Programme start: 2011

CICRP: Nicolas Bouillon

Partnership(s): Central Microscopy Facility of the University of Provence

Analysis of the constituent organic materials of paints (binders, varnishes, glues) of particular complex character as a result of the small quantity of the available sample and chemical modifications undergone by these materials during the course of ageing. It often involves the use of instrumental techniques that are particularly costly and at times difficult to carry out. The latter yield a very specific profile of the chemical composition of organic matter but only rarely determine its precise location in the stratigraphy of a pictorial layer.

In terms of the transfer of microscopy techniques from the biological and biochemical fields, the CICRP has witnessed, since the 1980s, the development of the use of histochemical techniques applied to the identification of organic material in cultural heritage property. It is in this context that the use of reactive fluorochromes under UV microscopy has expanded for the location and identification of organic material in the sampling of pictorial matter analysed as stratigraphic sections. In the first decade of the 21st century, this application has seen considerable developments with the arrival on the market of new reagents and new specific filters for microscopes, thereby heralding real progress in the effectiveness and accuracy of results.

Since 2009, the CICRP has gradually adapted its photonic microscopy equipment and carried out several testing campaigns on laboratory-manufactured and real samples. In 2011, tests carried out under confocal microscopes demonstrated the strong potential of this application. The work currently in progress consists in the finalisation of confocal microscopy protocols for the observation and interpretation of scientific reactions in organic material in paints. It consists first of all in studying the specificity of their autofluorescence before carrying out tests on fluorescence induced by specific fluorochromes.