Technical Diagnoses of Pigments and Applications in Historic and Contemporary Paintings: A Review of Literature

Over the past two decades, dealers, art historians and conservators in concert with recent developments in optical diagnostics, have sought to more fully understand what makes paintings unique to the artists who created them. Indeed, the press to identify and understand both the pigments as well as the application techniques that distinguish a genuine Rembrandt or an authentic Jackson Pollock, has gained momentum as more works enter the marketplace in the wake of escalating demand. The field of conservation as it relates to diagnosing characteristics of paintings seeks to establish scientifically-based technical analyses to the degree that unsigned, unauthentic, or erroneously cataloged works may be attributed with greater accuracy. Moreover, to many experts, the field of pictorial micro-examination employing various tests has helped to revolutionize conservation approaches and techniques which can then be adequately and judiciously applied to restoration efforts.

A number of advantages relating to technical diagnostics have come to be widely acknowledged. One of the boons of technical testing is the light it can shed on the intimate progression of how a particular painting evolved under a masterful artist’s brush. Indeed, in the instance of a deceased painter who perhaps made two copies of a masterpiece, diagnosing color application and composition in companion works can lend cross-referential insight into antiquated working methods beyond the viewer’s naked eye. In addition to expanding the depth of connoisseurship available to scholars, museums, dealers, and collectors, various types of diagnostics have entered the language of working artists themselves who have an interest in developing and refining their own paintings through a more thorough and scientific understanding of the techniques and materials that promote uniqueness and impact.

Despite apparent benefits and acceptance, the implementation of various kinds of pictorial diagnostics continues to stir levels of controversy. Interpretations of diagnoses and resultant restorations continue to come under scrutiny. Certain traditional authorities question the long term effects of the diagnostic procedures themselves. Yet, for many scholars and connoisseurs, the benefits outweigh the doubts, as diagnostic advances supplement rather than supplant the naked trained eye in interpreting the condition, quality, iconography, rarity, authenticity and subsequent dollar value of a painting. Techniques such as Synchrotron X-ray micro diffraction performed in Grenoble, France have yielded readings of complex elemental pigments that would be impossible to detect under the naked eye (Schreiner, Fruhmann, Jembirh-Simburger, Linke, 2004).

For those working either in front of the science or behind the curve of advances in the technical assessment of painted surfaces, some of the pressing issues that surround the field come in the form of questions:

• How does fluorescence microscopy go about sampling paintings for analysis?
• Can x-ray fluorescence spectroscopy (XRF) or Micro XRD be deleterious to fragile painted objects?
• What can be determined from scientific analysis of two seemingly identical paintings?
• Can other forms of scientific analysis such as mathematical sectioning and fractal optics be utilized in examining paintings?
• Are the discoveries from scientific studies on pigments and color only for the scientific community or can they be useful to working artists?

This review of literature on the diagnostics of determining the physical structure and chemistry of pigment application in contemporary and historic painting explores these five questions through the lens of articles and books by Schreyach, Aleson, de la Croix, and Aristides. Helping to round out the discussion, electronic databases of the Getty Museum Research Center join internet/database sources which also include studies conducted by Schreiner and his team at the Vienna International Centre for Diffraction Data. These resources join abstracts on pigment analysis including those conducted by Robin Clark at the University of London. It is important to note that the range of techniques that are used to assess paintings are also widely applied to the examination of sculpture, coins and other artifacts (Schreiner et al, 2004). Cited sources that accompany the annotated bibliography on Pageflakes provide documentation on various dimensional works in marble, bronze and terracotta.

• How Does Fluorescence Microscopy Go About Sampling Paintings For Analysis?

Conservation diagnostics minutely plumb not only the materials and chemicals layering the working ground and supporting structure of paintings, but analyze as well, any changes to works that may include painted additions, restorations as well as environmental impacts including age-related deterioration through layers of paint. Studies of paint layering are typically conducted through scraping off or excising a small physical paint specimen that houses a cross-section of strata. Embedding the sample in epoxy resin and subjecting it to fluorescence microscopy is generally productive in defining the structure of the layers (Schreiner et al, 2004).

• Can X-Ray Fluorescence Spectroscopy (XRF) or Micro XRD Be Deleterious to Fragile Painted Surfaces?

It has been argued that sample taking is deleterious to surfaces no matter how minute the particulate (Barabe, 2003). The Vienna Centre Diffraction paper acknowledges that since “chemical and many instrumental analytical techniques are destructive and require small samples to be taken from an object, the application of these methods upon objects of art and archaeology are severely limited nowadays." Interest in both X-ray fluorescence (XRF) as well as X-ray diffraction analysis (XRD) has increased in the last decades as both methods have proven to be sufficiently non-destructive if used with "care and respect to possible damage due to extensive radiation doses” (Schreiner et al, 2004). However, to many scientists, the primary advantage of present day methods of analyzing materials and methods of manufacture is that diagnostic techniques tend to avoid significantly touching artifacts. The non-invasive nature of the latest radiological technology is extensively discussed in the Getty article X-ray Fluorescence Spectroscopy (XRF) (Scott, 2003). Indeed, high energy beams have been determined to not immediately alter substrates of the canvas or pigments (Scott, 2002). However, century milestone effects of radiographic techniques have yet to be evaluated.

• What Can Be Determined From Scientific Analysis of Two Seemingly Identical Paintings?

Inconclusive evidence to the contrary, the significant advantages of technical diagnoses become immediately apparent upon examination of case studies. Certainly Aleson’s review of the Getty’s examination of dual portraits of the 18th century actress, Sarah Siddons, both painted by Sir Joshua Reynolds, reveals significant differences between canvases that were previously thought to be identical. Through a number of diagnostic techniques including x-ray fluorescence spectroscopy (XRF) it was determined that Reynolds expended much less detail on the portrait that hangs at Dulwich Picture Gallery in London as opposed to the one at the Huntington Art Collections in San Marino (Aleson, 1999). Advanced diagnostics revealed Reynolds changed his mind about color application in Siddon’s blue dress and thickly over-painted the garment to its present shade of golden brown. More importantly, microscopic examination revealed the binding medium of each of the canvases to be significantly different. “The Huntington version was painted in oil and oil-resin mixtures, in many layers of paint (sometimes as many as 20). The Dulwich version used a meglip-concoction - chosen to enable the later version to imitate the thick texture of the earlier picture” (Aleson, 1999). Thus, through advanced diagnostics, the artist’s evolution of his picture as well as his unique choices of color and paint chemistry, both of which had previously been hidden to the naked eye, became apparent. Indeed, through contacting databases of institutions such as the Getty, much useful information for working artists can be gleaned from careful study of the records from laser diagnostics.

• Can Other Forms of Scientific Analysis Such as Mathematical Sectioning and Fractal Optics Be Utilized in Examining Paintings?

Getting closer to the unique working methods of deceased artists has been the quest of experts as well as certain interested artists working today who continue to probe masterworks. Michael Cunningham, the Curator of Japanese and Korean art at the Cleveland Museum of Art, offers his viewpoint on assessing the creation of antique Japanese folding screens, and joins Juliet Aristides’ analytical discussion of how great painters of the past have orchestrated the picture plane (Cunningham, 2001). Artistides, who is an artist, joins other analysts who are keen to understand why some two-dimensional works are more optically pleasing than others. In an attempt to diagnose how color application is patterned on a picture plane, a full chapter in the author’s book, Classical Drawing Atelier, discloses the mathematical sectioning of a traditional canvas into what is known as the “Golden Mean” (Aristides, 2006). An artist’s unique propensity to create hidden “golden mean” abstract patterns in paintings that mirror natural organic ‘mathematical logarithmic fractal patterns’ found in nature, such as interrelated sea-shells, rose petals, and thumb prints, can help reveal the authenticity of an artist’s painting (Schreyach, 2007). Indeed, the presence of unique patterns in an artist’s technique constitutes an alternative form of signature (Aristides, 2006).

Varying methods of analyses can yield interesting results in the quest to establish specialized measures for authenticating canvases. Typically, as pointed out in both Schreyach (2007) and de la Croix (1970), authenticity rests with three factors: provenance, a list of a painting’s previous owners; connoisseurship, typically defined by the superior knowledge an expert possesses of an artist’s style that enables him to spot a fake; and material analysis which employs scientific methods that we have briefly discussed (de la Croix, 1970). Without subjecting paintings to radiological testing procedures, Schreyach leads a different approach to authenticity based on material analysis that references organic, biological science. Indeed, Schreyach’s approach attempts to find coordinates for the color lines Jackson Pollock uniquely applied to his canvases (Schreyach, 2007). It seems Schreyach is anxious to get hold of a new idea for material analysis since the introduction of twenty-four previously unknown paintings “putatively by Pollock,” puts pressure on seeking a radical new rubric that can verify Pollock through identically comparing his drip lines to photographic ‘fractal logarithmic patterns’ in nature. Schreyach outlines the idea that Pollock’s unique wrist and hand movements resulted in drip lines that are impossible for others to accurately replicate. In a sense, Pollock’s paintings are equal to his thumb print.

• Are the Discoveries From Scientific Studies on Pigmented Color Only For the Scientific Community or Can They Be Useful to Working Artists?

Not only does the unique application of paint internally “sign” a painting, but certain artists in the past utilized pigments that were composed of unique components. Contemporary analysis sheds light on these materials that can be of use to artists today. Indeed, chemical analyses that were predominant up until WWI have given way to techniques based on physics that have been developed to more deeply probe the identification of pigments (Clark, 2005). Raman microscopy, first used in 1928, has given rise to a technology that provides key “vibrational information on molecules in all states of matter including pigments, ions and lattice structures” (Raman and Krishnan, 1928). The advance of technology has greatly sped up and overhauled the original technique that utilized a “mercury arc as a radiation source and photographic plates as a detector,” upgrading to the use of “lasers as monochromatic polarized light beams of high irradiance that detect Raman signals from every kind of material” (Clark, 2005). Where colorants can occur in inorganic crystalline structures, XRD has proven the most effective method with which to clearly identify pigments (Schreiner et al, 2004). As a diagnostic technology, XRF joins XRD in proving effective in determining strong peaks for certain chemicals and elements such as arsenic, lead, and cobalt; witnessed in such projects as the restoration of an 18th century Koran, conducted by the Conservation Department of the State College of Buffalo. Indeed, testing revealed the crystalline structure for smalt, an ultramarine blue pigment made from ground glass (Beaty, 8). Indeed, such studies are important to present day artists who may wish to compound their own paints. In view of Raman microscopy, artists who work with color may be influenced to rethink their present ideas about pigments, coming to view them as almost living vibrational materials.

With new and sophisticated technological assessments, art experts and artists now have the advantage of scientific diagnostics to assist their inquiries into the chemical structure and application of pigments, broadening the scope of knowledge for the art of painting. Despite evidence from the Getty and other respected authorities, a problem perhaps still remains in the field of radiological diagnostics that awaits conclusive and incontrovertible evidence that proves such techniques will not play a part in the accelerated aging and degradation of the canvases that have come under testing; only time will tell. In the last decade, the advantages of employing scientific diagnostics to the application of pigments has outweighed the dangers, as more artifacts suffering from the ravages of time have increasingly required expert restoration. To date, technical diagnostics have significantly aided the effort to salvage our global cultural heritage and continue to enrich the knowledge of those involved in the creation of new work.


References

Aristides, Juliet, (2006). Classical Drawing Atelier. New York: Watson-Guptill.

Asleson, Robyn, (1999). A Passion for Performance: Sarah Siddons and Her Portraitists. Getty Museum Publications Newsletter 14.1. Retrieved June 17, 2009, from http://www.getty.edu/conservation/publications/newsletters/14_1/gcinews01.html.

Barabe, Joe, (2003). The Microscope in Art Conservation and Authentication Studies. True Colors. Retrieved July 3, 2009, from http://www.modernmicroscopy.com/main.asp?article=27.

Beaty, Katherine, (2005). 21st C. Remedies to 19th c. Repairs of an 18th c. Koran: Materials Analysis, Treatment and Housing. Retrieved July 3, 2009, from http://www.ischool.utexas.edu/~anagpic/pdfs/Beaty.pdf.

Clark, Robin, J.H., (2005). Raman Microscopy in the Identification of Pigments on Manuscripts and Other Artwork. (Sackler NAS Colloquium) Scientific Examination of Art: Modern Techniques in Conservation and Analysis. Retrieved July 4, 2009, from http://books.nap.edu/openbook.php?record_id=11413&page=162.

Croix, de la, Horst, ed. (1970). Gardner’s Art Through the Ages, Fifth Edition. New York: Harcourt, Brace & World.

Cunningham, Michael, (2001). “Reverie on a Pair of Japanese Screens.” The Magazine Antiques, 108-113.

Raman, C.V., & Krishnan, K.V. (1979). History of the Discovery of the Phenomenon of Raman Light. Journal of Applied Spectroscopy Vol. 30, 510-515.

Schreyach, Michael, (2007). I am Nature: Science and Jackson Pollock, Apollo 35.

Scott, David, (2002). The Application of Scanning X-Ray Flourescence Microanalysis in the Examination of Cultural Materials, Archaeometry 44.

Scott, David, (2002) X-Ray Flourescence Spectroscopy (XRF). Retrieved July 3, 2009, from http://www.getty.edu/conservation/science/about/xrf.html.

Schreiner, M., Fhrümann, B., Jembrih-Simbürger, D., Linke, R. (2004). X-Rays in Art and Archaeology - An Overview. Institute of Humanities, Sciences and Technologies in Art/Advances in X-Ray Analysis, Vol. 47. Retrieved July 3, 2009, from http://www.icdd.com/resources/axa/vol47/v47_01.pdf.♦