By Derek Moss
On Monday 13th June, Professor Austin Nevin, chemist, conservator and researcher at the Institute of Photonics and Nanotechnologies (IFN), as well as coordinator of various research groups, committee member of various conferences, and co-author of over 40 publications, gave a very interesting technical and illustrated talk on the analysis of paintings and painting materials using optical, molecular spectroscopic and imaging techniques, which have produced invaluable revelations into the creation of some of the world’s best-known artistic wall painting masterpieces by Masolino da Panicole and Leonardo da Vinci, to the watercolour painting on paper by Vincent Van Gogh.
This talk, organised by Flimkien għal Ambjent Aħjar, had come about as part of FAA’s heritage project to restore the late Medieval ‘Madonna of Mercy’ 4-panel altarpiece at St Mark’s Augustinian Priory, Rabat, which is supported by BANIF Bank, and was held at the Chamber of Commerce Courtyard in Valletta.
As conservator, Professor Nevin stated that conservation was not just about the ‘repair’ of old paintings, but initially posed questions such as ‘how was the work painted’?, ‘what materials were used’?, ‘has it been restored’? and ‘has it been moved’? He stated that in the 1920s a movement to clean old paintings caused a lot of damage by over-aggressive cleaning which wiped out anything that was not well adhered. Therefore many of the backgrounds and even clothes of the subjects were lost. Prof. Nevin stated that his research work on works of art is carried out alongside engineers, chemists, architects and conservators all working together in the interpretation of acquired data. Usually acquisition of data is by the lab visiting the painting’s location, where as much information as possible is extracted, using microscopic, spectroscopic and data analysis techniques.
Professor Nevin discussed three paintings as examples of his research work. First discussed were the 1435 wall paintings (frescos) in the Baptistery at Castiglione Olona, Italy, of the “Life of St. John the Baptist” by Masolino da Panicole, upon which non-invasive analytical techniques were used. These include UV Fluorescence to determine traces of pigments and minerals in paint which fluoresce under UV light, Multispectral Fluorescence Imaging which uses filtered UV light to acquire numerous images at different wavelengths from the surface of the painting, which were mapped to record the variation in intensity of many colours including red hues from cochineal which have faded. Also, to identify the elements of each layer means to identify not only the hues but also the source of dyes pigments used, like lead, cochineal beetles (red), brazil wood (purple), kermes (red, crimson), and lake (lac) pigments such as madder lake (rose, red) and other lake pigments prepared by precipitating the dye extract with aluminum salts, such as alum. All pigments are light sensitive, so another non-invasive analytical technique called Fluorescence Lifetime Imaging (FLIM) is used, which is an imaging technique used to measure the exponential decay over time of luminescence / fluorescence from media and lakes used in paintings, and to identify organic compounds, such as oil added to tempera, that are present in the artwork.
Note: Organic materials show fluorescence emission after being excited by UV radiation, whereas inorganic nature of pigments absorb UV radiation, so do not fluoresce.
Another very efficient and non-destructive technique used in the investigation of works of art is Raman spectroscopy, which provides identification of the molecular components in individual pigments and their degradation products. This leads to insights into the working method of the artist and allows information to be gained about the original state of the painting at the time of its creation in cases where the pigments were degraded with age. Finally, analytical measurements of microsamples identify the chemical composition of other materials under investigation, such as glue and stucco left from earlier restorations in response to the decay state of the painted walls.
The second painting discussed was the 1494-1498 wall painting in the Convent of Santa Maria delle Grazie, Milan, entitled “The Last Supper” by Leonardo da Vinci. Prof. Nevin explained that not much is known about how Leonardo painted it, but we do know that he used very expensive pigments, many of which were so expensive that they would have been ordered specially for him, like the gold on Judas’s vestments. Leonardo spent many, many hours planning and painting details which would not be seen from a distance, by the friars as they dined in the refectory, such as the reflections of the lustre on plates and the glassware.
The question arose as to why the painting of the “Last Supper” deteriorated so rapidly when other paintings of a similar era have survived in a much better state. It seems like the unfavourable Milanese climate had contributed to the deterioration of the painting within decades of its completion. This work is not a straightforward fresco as it is applied on a complex base of many layers, in contrast to other frescos which usually have 1 or 2 layers of paint. Leonardo experimented with creating an impermeable oil-based ground by mixing lead oxide with oils in an attempt to make the painting resist the rising damp in the wall. Pigments ground down finely were mixed with waxes in order to apply them to the wall, and were also used in overlays to reflect through in different ways. Blues would be created not just by using lapis lazuli (ultramarine), which was an expensive pigment imported into Europe from mines in Afghanistan, but by mixing it with black, painting blue on black, white or mixing it with red lake pigments. It appears that Leonardo’s “Last Supper” was submerged underneath six layers of restoration. The first restoration was done in 1726 and the last restoration done in 1999. As each layer of misguided restoration was added, originally rosy-cheeked and beautiful St. Matthew turned into a bearded old man.
The third painting briefly discussed was the watercolour on paper entitled “The Breton Women” by Vincent van Gogh, on display at the Civica Galleria d’Arte Moderna, Milan, Italy. Studies of “The Breton Women” using imagery as used in the study of Masarino revealed widespread use of ‘glow in the dark’ pigments. This turned out to be due to the presence of copper and silver impurities in the early zinc oxides used for painters’ pigments. Having discovered this, it then became apparent that this phenomenon was present in other paintings of the same era, such as the watercolours of Lafarge. Pigments commonly used by Van Gogh were synthetic ultramarine (blue), cinnabar / vermilion (red HgS – mercury sulphide), and chrome yellow (PbCrO4 – lead chromate). Because the latter pigment tended to oxidise and darken on exposure to air over time and it contained lead, a toxic, heavy metal, it was originally replaced by another pigment, cadmium yellow, which when mixed with enough cadmium orange produced a colour equivalent to chrome yellow.
Prof. Nevin concluded his talk by stating that wall paintings (frescos) are complex, in-situ analysis gives more information about stratigraphy and degradation, and molecular spectroscopy gives identification of colourants.
Attendance at this event exceeded all expectations, not only by FAA members, but also non-members interested in the history of art, including numerous students.