31 stage also included the removal of a scattering of older retouchings. Their removal revealed only very slight damage and paint loss beneath. During the cleaning, the conservation team noticed that in the left-hand edge of the overpainted background, close to the curtain rail, the upper paint layers reacted very differently to the solvents than the original paint layers directly beside them. This was again observed at several sample sites in the area between window casement and curtain, and led to Christoph Herm of the Science and Archaeometry Laboratory at the Dresden University of Fine Arts being called in to conduct a series of scientific investigations.17 The results of these colour sample investigations were astonishing, for they called into question the previously roundly accepted assertion that Vermeer had himself carried out the overpainting of the background motif of the Cupid picture. Two samples in particular from the area of the background picture [samples H8-Q and H9-Q, see p. 52, scheme of the colour samples, fig. 3] proved decisive for this assessment. They showed that there were two layers of binding medium over the ivory-coloured ground coat and the thin original tinted imprimatura. In the sample H9-Q shown (see p. 56, fig. 9 a+b), a thin dark layer is visible between these layers of binding medium, and this could only be identified as a layer of (surface) dirt. Above these layers of binding medium, which mainly contain natural resin and thus should be interpreted as old layers of varnish, there are two layers of overpaint. Lying on top of these was one final layer, the uppermost layer, which represented the same varnish that had just been removed in the period of time since the taking of the sample. All eyes now turned towards the layers of binding medium between the original paint layer and the layer of overpaint. Since the cleaning had also revealed the presence of overpainting along all four edges of the Girl Reading a Letter, further paint layer samples [samples H18-S, H14-Q, H20-Q, H21-S, H22-S, H23-S, see p. 52, fig. 3] were taken in these marginal areas and compared with the findings of the background picture. Here, too, we saw that there were old layers of binding agent between the original paint layer and the overpaint. These new findings concerning the stratigraphy of the background picture were backed up by the macroscopic X-ray fluorescence scanning (MA-XRF) of the entire painting, whose results are discussed in detail in the chapter on painting technique (pp. 58–72).18 Added to this tests, such as solubility tests, establishing differences in the solubility behaviour of the paint layers, and point analysis, examining the paint layers at isolated sample sites, a number of further observations were made. It was observed that the tone of the overpainted area changes from a warm grey at the lower edge to a dark brownish-grey higher up. This colour gradation is particularly conspicuous when compared to the white of the wall to the right of the girl’s back. This difference in colour, which was greatly intensified by the removal of the varnish, could not have been a consequence of the natural ageing of the paint. It was due instead to the colour of the paint later used for the overpainting, which had been selected at the time to match the brownish-yellow tone of an already aged layer of varnish that lay over Vermeer’s painting. These colour differences and inconsistencies in tonality were an indication that there was an interval of at least several decades between Vermeer’s execution of the work, around 1658, and the application of the overpaint. During this intervening period the first (original) varnish layer dried and underwent significant yellowing as it aged. At the same time, a layer of surface dirt and debris settled on top of it. At some point a second varnish layer was applied. Finally, the overpaint layer was applied to the area of wall behind the girl, completely covering up the background Cupid picture for centuries until now (figs. 14–16). Fig. 13 Detail with scratch on the Cupid’s shoulder
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