Since its completion by Vincent van Gogh, the Amsterdam Sunflowers has been the subject of a complex history of interventions. Combined with the natural ageing and deterioration of the materials used by the artist, this has strongly affected the present appearance of the painting. The materials and techniques used in Sunflowers and related colour changes have been presented in chapters 4 and 5. This chapter focuses on characterizing the non-original surface layers present as well as secondary compounds arising from pigment-binder interaction in original paint components. The outcomes of this research help to reconstruct the restoration history of the painting and to understand its present condition, as a basis for optimizing future conservation treatment (as elaborated in chapter 7).
In keeping with Van Gogh's usual practice in the period, he left Sunflowers in an unvarnished state. Today, however, multiple layers of varnish are present. These have yellowed and make the painting appear highly glossy, whereas originally it presumably had the more subtle satin gloss related to pure oil paint. Conversely, some areas of the painting now look matt, since wax has been locally applied in the past.
Historical records provide sparse information regarding the surface layers added during earlier campaigns of treatment (see chapter 7). We know that the painting was varnished in 1927 by the conservator Jan Cornelis Traas, as part of a broader restoration and structural (lining) treatment. Remains of paper tape on the tacking margins of the painting are believed to date from this period (see chapter 7, p. 184). Further documents record that in 1961, Traas worked on the painting again. However, as there is no known account of what this treatment entailed, it remained in question whether Traas removed the 1927 varnish and/or applied new surface coating layers instead. Furthermore, in the late twentieth century, wax was applied in certain areas, used to matt down the glossy varnish and/or impregnate and consolidate the ground.
This chapter describes the outcome of the technical examinations of the Amsterdam Sunflowers, characterizing the surface layers present and assessing the history of application as revealed by their stratigraphy and chemical composition.