Investigation of discolouration in depicted foliage in five 17th century landscape paintings

Detail of the foliage depiction in a landscape painting by Sebastian Vrancx. The glazes in the area of the foliage depiction appear partially dark brown or light brown, they are present next to light green layers of paint. (Image: TH Köln - CICS - Charlotte Hoffmann)

This Master thesis focussed on technical analysis of depicted foliage in five 17th century landscape paintings in the collection of the Wallraf-Richartz-Museum & Fondation Corboud. Some areas of foliage depicted in these paintings appear to be browned. The aim of the project was to investigate whether this appearance is the result of colour changes and which mechanisms might have caused them.

At a glance

Kategorie	Beschreibung
Student project	Investigation of discolouration in depicted foliage in five 17th century landscape paintings
Supervisors	Prof. Dr. Ester Simoes B. Ferreira
Student	Charlotte Hoffmann (M.A.)
CICS department	Natural Sciences
	Paintings, Sculptures and Modern Art
Project partners	Dipl. Rest. Iris Schaefer Wallraf-Richartz-Museum & Fondation Corboud, Cologne
Duration	09/2017 - 02/2020
Location	CICS / University of Applied Sciences Cologne

Picture gallery

Detail der Laubdarstellung in einem Landschaftsgemälde von Roelant Savery. Die Lasuren im Bereich der Laubdarstellung erscheinen dunkelbraun.

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Roelant Savery "Animals in a forested mountain landscape", 1629. Detail of the foliage depiction, which appears browned. (Image: TH Köln - CICS - Charlotte Hoffmann)

Mikroskopaufnahme der Laubdarstellung in einem Landschaftsgemälde von Roelant Savery. Die Lasuren erscheinen dunkelbraun, es liegen blaue Pigmentpartikel in einer verbräunten Bindemittelmatrix vor.

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Roelant Savery "Animals in a forested mountain landscape", 1629. Microscope images of the dark brown foliage depiction, blue pigment particles are present in the browned binding medium. (Image: TH Köln - CICS - Charlotte Hoffmann)

Mikroskopaufnahme des Querschliffs einer Probe aus der verbräunten Lasur in der Laubdarstellung des Gemäldes von Roelant Savery. Die Farbschicht erscheint bräunlich, es liegen blaue Pigmentpartikel in einer verbräunten Bindemittelmatrix vor. Detail a zeigt ein Rückstreuelektronenbild des Ausschnitts, Detail b zeigt die gleiche Stelle im Auflicht. Detail c bis f zeigen die Elementverteilung von Kupfer, Calcium, Aluminium und Blei.

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Microscope image of a cross-section of a sample taken from the browned glaze in the foliage depiction in the painting by Roelant Savery. The paint layer appears brownish, with blue pigment particles embedded in the browned binding medium. Detail a shows a backscattered electron image, detail b shows the same area in reflected light. Details c to f show the element distribution of copper, calcium, aluminium and lead. (Image: TH Köln - CICS - Charlotte Hoffmann)

Tabular representation of the ageing of two paint swatches. The left side shows the paint consisting of a mixture of azurite and yellow lake in linseed oil, and the right side shows the paint consisting of azurite in linseed oil. The top row shows the paint swatches before ageing, the middle row after ageing under ambient condition and the bottom row after cyclic accelerated ageing for eleven weeks. The colour change from green to brown is clearly visible in the paint with azurite and yellow lake.

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Photographs of paint swatches to illustrate the colour and ageing properties of mixtures of the presumably used pigments in linseed oil. A colour change from green to brown can be clearly seen in the paint containing azurite and a yellow lake in the course of ageing. (Image: TH Köln - CICS - Charlotte Hoffmann)

In her Master project, Charlotte Hoffmann examined foliage depictions in five 17th century landscape paintings within the collection of the Wallraf-Richartz-Museum & Fondation Corboud. Starting point of this art-technological examination was the observation that areas of depicted foliage appeared to be discoloured. The objective was to investigate whether colour changes are present in the areas that appear browned and subsequently to hypothesise on the mechanisms causing this colour change.

The selected landscape paintings were examined microscopically and with analytical methods on micro-samples. Obtained results clearly show that colour changes have occurred in the examined brown areas. The composition of these discoloured paint layers differs from the intact green and intentionally red-brown paint. Mixtures of azurite and a presumably originally yellow lake pigment were used as colourants.

Based on these results, paint outs were prepared and artificially aged to reconstruct possible ageing mechanism. Results support the hypothesis that the browned areas were originally intended to be dark green. The browning is probably mainly due to the high binder content and the associated ageing mechanisms.

Contemporary written sources support the assumption that the examined glazes are discoloured. In the studied text passages, mainly green colours and corresponding pigments or mixtures were described for foliage in landscape paintings. An exception is the depiction of wilted foliage, however, the pigments indicated for this purpose were not detected in the examined paint layers.
In summary, the results of this study contribute to the understanding of the examined landscape paintings in their aged state. The Master project led to a doctoral research project investigating choice of materials, techniques, intended colour effect and colour changes in foliage depictions in 17th century paintings. Since September 2020, Charlotte Hoffmann has been a doctoral student in the interdisciplinary Graduate Research Programme ‘Changing Frames’ at University of Konstanz in cooperation with the State Academy of Fine Arts Stuttgart, funded by the Volkswagen Foundation.

The Master thesis was supervised by Prof. Dr. Ester Ferreira and Dipl.-Rest. Iris Schaefer. Charlotte Hoffmann received a scholarship from the Studienstiftung des deutschen Volkes (German Academic Scholarship Foundation) from March 2019 to June 2020. Main parts of the results of the investigations were published in the Zeitschrift für Kunsttechnologie und Konservierung in 2021.