PROPAINT Improved Protection of Paintings during Exhibition,Storage and Transit Final Activity Report

This article presents a case study regarding the analyses of white deposits that formed on the inside of the glass of the microclimate box in which Gerrit Dou, The Young Mother, 1658 (Mauritshuis inv no 32), was housed. Deposits corresponding to dark reddish brown and black areas of the painting were seen to form over a period of a few months, from March to July 2007, when the picture was hanging on an exterior, southwest facing wall. FTIR and EDX analyses (ICN, Amsterdam) revealed that the deposits consist of sodium soaps, most likely in the form of sodium palmitate and stearate. Precise monitoring of the climate conditions carried out in the gallery by Technical University of Eindhoven (20042006) demonstrated temperature fluctuations on this wall as high as 31 ̊C with a corresponding variation in relative humidity from 31-80%. It is hypothesised that a temperature gradient developed inside the microclimate box as a result of contact with the warmed wall and/or exposure to direct sunlight, causing free fatty acids to evaporate out of the paint. The deposition of fatty acids on the inside of the glass is considered to undergo a subsequent reaction with the sodium in the glass to form sodium soaps. The results correspond with earlier published studies regarding ghost-or transferred images on the inside of glass and fatty acid deposits found on the surface of paintings. Introduction Paintings in the Mauritshuis are routinely glazed with protective glass to prevent damage from vandalism and accidental damage. Since the early 1990s, panels that are deemed fit to travel, are also regularly sealed in specially adapted frames to minimize climate fluctuations so called microclimate boxes. The microclimate box currently in use in the Mauritshuis was developed in the early 1990s by Jørgen Wadum (Wadum et al. 1994; Wadum 1995). The microclimate box is produced in house by the framing technician, and is constructed within the existing frame, in which safety glass 4 is held in place on the inside of the frame rebate with aluminium tape, and sealed with a transparent polycarbonate (Lexan) backboard, which is also sealed with aluminium tape. If the rebate is not deep enough to accommodate the glass, balsa wood spacer, felt and painting, it is necessary to extend the rebate with a build-up on the 4 A thickness of 4 mm Schott Mirogard Protect safety glass is used in the Mauritshuis for microclimate boxes. Mirogard Protect is made of two sheets of low iron float glass with anti-reflective coating on one surface, laminated with a special UV-absorbing interlayer. For data see: http://www.schott.com/architecture/english/download/datenblatt_mirogard_englisch.pdf?PHPSESSID=jte2a46jc n51f6qjen5gvmbf16 PROPAINT project Final Report 150 reverse of the frame (fig. 1). No sorbent material is added; the buffering role of the panel is considered sufficient. Acclimatisation of the painting in the correct relative humidity is critical for the conditions in the microclimate box. Fig. 1. Diagram showing cross-section of the construction of microclimate boxes used in the Mauritshuis. Over the course of many years it has been observed by conservators in the Mauritshuis that hazy deposits regularly form on the inside of the glass. This has also been observed in other museums which glaze their paintings. These hazy deposits, often referred to as ghosttransferredor mirror images, are disturbing and can severely obscure the art work. Often these deposits are associated with the image, hence the term mirror images (Williams 1988; Skaliks 1999). The hazy deposits are greasy in nature and depending on thickness, are greyish or whitish in appearance. In the Mauritshuis they are removed periodically by the framing technician, first with water and green soap 5 using a micro-fibre cloth, followed by wiping with ethanol and damp paper. Concern has developed as to the recurring nature of the deposits and the long term effect on paintings. The reoccurrence of deposits has implications for the microclimate box design and climate conditions in certain locations in the museum. Regular removal of the deposits has furthermore significantly increased the work load for the technical staff: since 2001, when cleaning of the glass began being recorded, hazy deposits on more than 200 paintings have been removed. Monitoring of climate conditions in the Mauritshuis During the last renovation of the museum in 1984-86 the museum was equipped with a modern air conditioning system. Between 2004 and 2006 the Mauritshuis along with several other museums participated in a research project Project Klimaat Onderzoek Rijksmusea initiated by the Erfgoedinspectie. As part of this project the University of Eindhoven (TU/e) was commissioned to monitor the climate conditions in a number of museums including the Mauritshuis (Baan and Duijnhoven, 2005; Marten, Schellen, van Schijndel, Van Aarle, 2007). The various museums were chosen because of their inherently different building type, 5 Green soap is a weak soap used for household cleaning with a green colour made with plant oil and potassium hydroxide (instead of sodium hydroxide, as is the case for hard soaps). http://nl.wikipedia.org/wiki/Groene_zeep PROPAINT project Final Report 151 collection and type of climate installation. For the Mauritshuis, the combination of a monumental historic building with a relatively modern climate installation was considered a valuable case study. The final results of this research were published in 2007 (Meul, V.L.B.M. 2007). In the Mauritshuis, the exhibition galleries are located on the ground and first floors. Exterior walls in each of the corner galleries contains concealed windows which consist of singleglazed windows closed off with an infrared-absorbing screen and a sheet of Lexan. In the galleries these windows are concealed behind fabric-covered, fire retardant 10 mm construction sheeting. Fig. 2 shows the locations of the concealed windows in the first floor galleries. Despite the uniformly conditioned air supplied to each floor of the museum, measurements recorded by TU/e demonstrated strongly varying temperatures and relative humidity in several of the galleries, depending on their orientation with respect to the sun. Galleries facing southwest were shown to have more variation in temperature compared to the galleries facing northeast. 6 Fig. 2. Floor plan of first floor galleries in the Mauritshuis (from Baan and Duijnhoven 2005). The concealed windows are marked in blue. The location of Dou‟s, The Young Mother between February and July 2007 in the early Rembrandt gallery (1.4), is marked by the red dot. Case study in The Mauritshuis Gerrit Dou, The Young Mother (MH inv no 32) Oil on panel Signed and dated: GDOV 1658 73.5 x 55.5 cm 6 Marten, Schellen, van Schijndel, Van Aarle 2007, pp. 69-111. For cross-section of the construction of the concealed windows, see fig. 5.12 p. 75. PROPAINT project Final Report 152 Fig. 3. Gerrit Dou, The Young Mother, 1658, panel, MH inv no 32 Physical build-up of the painting Gerrits Dou‟s The Young Mother, which is painted on a radially cut, single oak plank retains its original thickness and format. The painting appears to have a chalk and lead white ground possibly with the addition of a little umber or black. It has been noted that in some crosssections the ground now has a brown appearance, which may point to saponification of the lead white particles. In the X-ray, the ground is faintly visible and appears to have been applied with horizontal strokes. Paint cross-sections studied by Groen and Struick van der Loeff demonstrate a multiple layer build-up of numerous thin paint layers. As many as twelve layers of alternating brown and black layers were found in some paint cross-sections. 7 In their study of the dark background paint (using EDX) they identified a high proportion of chalk, along with umber, red ochre, bone black and a little lead white. Wrinkling and wide drying cracks, which are very pronounced in the upper part of the painting are often encountered in Dou‟s dark paint layers, and clearly point to drying problems. This can be explained by the use of multiple oil-rich layers that contain poor-drying pigments, such as asphalt and carbon/ bone black, possibly in combination with slow-drying walnut oil. 8 In Languri‟s research into the effect of some of these organic black and brown pigments on the drying of oil, asphalt was 7 Struick van der Loeff and Groen 1993, p. 101-102. 8 Struick van der Loeff and Groen 1993, note 14 p.103. In 1986 Raymond White, National Gallery, London using gas chromatography identified asphaltic material in the binding medium of The Young Mother by the presence of hopane-like triterpines. In Dou‟s Lady at her Toilet, 1667 (Museum Boijmans van Beuningen) the the presence of phenol suggests the use of Kassel earth in the dark paint layers. See Boersma 2000, pp. 5960 and note 24 p. 63. PROPAINT project Final Report 153 found to retard the drying process, whereas (pure) Kassel earth (a lignitic pigment) is expected to exert a siccative effect (Languri 2004).