Mr. Douglas MacLennan Profile

Douglas MacLennan

at Getty Conservation Institute

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Author

Publications (2)

Proceedings Article | 22 July 2019 Presentation

The study of the degradation of cadmium yellow paints through their photoluminescence emission from trap states (Conference Presentation)

Daniela Comelli, Marta Ghirardello, Gianluca Valentini, Austin Nevin, Douglas MacLennan, Alan Phenix, Catherine Schmidt Patterson, Herant Khanjian, Karen Trentelman, Lucia Toniolo, Aviva Burnstock, Markus Gross

Proceedings Volume 11058, 1105806 (2019) https://doi.org/10.1117/12.2525582

KEYWORDS: Cadmium sulfide, Cadmium, Luminescence, Semiconductors, Imaging spectroscopy, Microscopy, Spectroscopy, Carbonates, Crystals, X-rays

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The industrial developments of the 19th century included the production of a variety of synthetic pigments and dyes, which were often used by artists who were not concerned with their stability over time. Among these pigments, cadmium yellow, based on cadmium sulfide (CdS), was popular with artists beginning in the mid-19th century. This pigment may discolour or darken and/or exhibit loss of adhesion and formation of white globules on the painting surface [1-2]. Its degradation involves photooxidation of CdS and the formation of degradation products (sulfates, oxalates, and carbonates) [1-4]. However, not all historic paints containing cadmium yellow degrade. It appears that CdS paints produced between the late 19th and early 20th centuries are particularly prone to degradation, as has been documented in paintings dating from 1880 to 1920 [4]. Because these paintings have been exposed to different environmental conditions, it has been speculated that the degradation of cadmium yellow may be related to imperfect syntheses, resulting in the formation of a more reactive form of CdS. However, the link between the presence of these reactive pigments and the tendency of the paint to deteriorate is not well understood. CdS is a IIb-IVa semiconductor. When excited by light of an appropriate energy, the semiconductor exhibits a characteristic near band edge (NBE) emission, closely related to the CdS energy bandgap, and emission from intra-bandgap trap states (TS) related to crystal defects [5-6]. Even though little considered when dialing with luminescent paints, the TS emission can provide useful information about surface states in nanocrystalline semiconductors [7]. Moving from nanoscience to conservation studies, the detailed investigation of TS emission in CdS paints is proposed here to probe changes in the density and energy of surface defects and ultimately in the surface reactivity of CdS following degradation. Photoluminescence imaging, microscopy, and spectroscopy – complemented by other X-ray based spectroscopies and microscopies – have been used to examine historical and modern manufactured CdS-based paints following artificial aging. Lastly we investigated the degradation of cadmium yellow paints in the painting Femme (Époque des “Demoiselles d’Avignon”) (1907) by Pablo Picasso. This study found that in degraded CdS paints the TS emission is much higher in intensity (with respect to NBE emission) and shifted to shorter wavelengths with respect to preserved paint layers. This observation indicates a higher density of TS in the degraded paint, which promotes the surface reactivity of CdS particles and the subsequent paint degradation. In general, results indicated that the analysis of TS emission is a highly sensitive method for identifying early signs of degradation in CdS paints. [1] Van der Snickt, G. et al., Anal. Chem. 2009, 81 (7): 2600–2610 [2] Mass, J. et al., Analyst 2013, 138: 6032–6043 [3] Anaf, W. et al., Dyes and Pigments 2015, 113: 409-415 [4] Monico, L. et al., Chemistry–A European Journal 2018, 24.45 [5] Cesaratto, A. et al., Analytical Methods 2014, 6.1: 130-138 [6] Rosi, F. et al., Microchem. J. 2016, 124: 856-867 [7] Krause, M. M. et al., Phys Chem Chem Phys 2015, 17:18882-18894.

Proceedings Article | 22 July 2019 Presentation

Analysis of the physical characteristics and chemical composition of gold leaf in works of art by scanning macro x-ray fluorescence (MA-XRF) spectroscopy (Conference Presentation)

Douglas MacLennan, Arlen Heginbotham, Monica Ganio, John Delaney, Lynn Lee, Laura Llewellyn, Karen Trentelman

Proceedings Volume 11058, 110580Y (2019) https://doi.org/10.1117/12.2526230

KEYWORDS: Gold, Chemical analysis, X-ray fluorescence spectroscopy, Spectroscopy, Fluorescence spectroscopy, Visualization, Data modeling, Manufacturing, Materials analysis, Trace element detection

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With its intrinsic preciousness, symbolic, and aesthetic connotations, gold leaf was essential to the decoration of artworks from antiquity to the Renaissance. Despite this importance, the physical characteristics and chemical composition of gold leaf in works of art have not, to date, been extensively studied. In this work, case studies from a number of works of art demonstrate the ability of scanning macro X-ray fluorescence (MA-XRF) spectroscopy for in situ, non-invasive examination of the physical characteristics and the elemental composition of historic gold leaf in works of art in different media. Macro-XRF scanning has opened up new avenues of research by providing insight into how these micron-thin sheets of gold were manipulated and applied in individual objects [1,2]. Besides elemental composition, data provided by MA-XRF on gilded objects includes the visualization of the shape, size, and application techniques of individual gold leaves. For example, measurements of the dimensions of individual gold leaves obtained directly from XRF map data of thirteen 14th and 15th century Italian panel paintings reveals differences in the dimensions of gold leaf across different administrative regions throughout the Italian peninsula during this period. This work suggests a deterministic system of leaf production, which varied between the city-states, controlled by the different city guilds. In addition to leaf dimensions, a comparison of the degree to which gold leaves were overlapped during the gilding process reveals important clues about the artistic hand of individual artists. Overlap measurements appear consistent between artworks ascribed to the same artists, even when that artist is gilding with gold leaf of different dimensions, but differ between artworks painted by different artists. Taken together, these measurements advance art historical scholarship by providing a material understanding of artistic practice. In addition to elucidating several facets of the original artistic creative process, XRF maps have also helped identify subsequent interventions, providing new evidence of possible historic conservation or restoration efforts. Our knowledge of how gold leaf was manufactured is based on historical treatises rather than material analysis. The ability to confidently detect variations in minor and trace elements in historical gold leaf may provide new tools to better understand dating, location of production, and trades. The suitability and inherent limitations of MA-XRF for the semi-quantitative analysis of the gold leaves, based on a feasibility study using a set of modern gold leaf samples will also be discussed. A ground truth for the concentrations of these, and other trace, elements was validated using inductively coupled plasma-mass spectrometry (ICP-MS). Linear regressions for gold, silver, and copper provide a model for relating XRF intensity to concentration that can be tested on the XRF map data obtained from the historic artworks. [1] D. MacLennan, L. Llewellyn, J.K. Delaney, C. Schmidt Patterson, Y. Szafran, K. Trentelman, “Visualizing and measuring gold leaf in 14th and 15th century Italian gold ground paintings using scanning macro X-ray fluorescence spectroscopy (MA-XRF),” Heritage Science, Submitted (2019). [2] D. MacLennan, L. Llewellyn, “Visualizing and measuring gold leaf: Case Study: Gentile da Fabriano,” The Burlington Magazine, Submitted (2019).

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