Paint analysis as a tool for understanding artistic process

Libby Sheldon, Lecturer in History of Art with Material Studies, UCL

Making Art in Tudor Britain
Abstracts from Academic Workshops (2007-8)
Funded by the Arts and Humanities Research Council

Technical analysis of paintings is always a voyage of discovery, and close examination of the paint by stereo microscopy and sampling has led to unexpectedly rich findings. Investigation of the paint layers was determined by art historical questions and queries arising from all the various forms of analyses. Why did the X-ray plate of Gerlaacht Flicke's Self-Portrait with Strangwish (NPG 6353) appear featureless and opaque? A cross-section showing a thick layer of lead white applied over the panel support, in addition to lead white over the parchment or paper, explained the blank image in X-ray. The priming of both panel and parchment suggests that the painting was executed on parchment or paper while Flicke was in prison, and stuck down onto the prepared wood later.

Examining Baron Berners by Ambrosius Benson (NPG 4953) to confirm the presence of lead-tin yellow, led to a chance find when the sitter's puzzlingly dull, brownish purple robe was sampled. Could it have been brighter when first painted? Was it an optical mixture of charcoal blue-black and red, or the once luxurious purple produced by smalt and crimson lake, such as that found on the curtain in Flicke's portrait of Thomas Cranmer (NPG 535)? Surprisingly it proved to be fluorite: a rarely found pigment, although current research (eg. Marika Spring, National Gallery London) suggests there might have been sources in England as well as the Austrian Tyrol. Such finds open up broader avenues of research. Did fluorite have an exotic rarity amongst artists in the 1520s? Does it have an iconographic relationship with the sitter? Analysis of the mixed purple in Thomas Cranmer demonstrated another major issue of the project ­ the original condition of the paintings. The deterioration of this purple raises issues of its original symbolism and the whole compositional balance.

The investigation of paint not only identified materials, but sought evidence of the reason for their employment. What was the purpose of the azurite imprimatura found under two Master John paintings, for instance? And what is the significance of the vermilion, included in the azurite blues of Flicke's two paintings? A relatively expensive pigment, vermilion's even distribution in the blues is unlikely to be accidental. Was he attempting to imitate the more expensive and important ultramarine, or was his supplier to blame for the addition? Why were there two layers of silver leaf in the construction of Master John's Edward V1 (NPG 5511)?

Technical analysis is not an exact science but a new form of connoisseurship, and interpretation is critical. The significance of such findings as fluorite, or the red in blue will only be understood in the context of both material and general art history. This project, sharing information at every point between those examining the paintings (making the initial selection and interpretation of samples) and the scholars of the period, has opened up the possibilities of full and productive discussions of the data.