New insights into the materials of fifteenth- and sixteenth-century Netherlandish paintings in the National Gallery, London

The long-term programme of technical examination conducted at the National Gallery, London, during cataloguing of the Netherlandish School paintings surveyed the materials and techniques of a wide range of artists, including not only Van Eyck, Van der Weyden, Bosch, Bruegel, Massys and Gossaert but also lesser known painters from the same period. The research presented in this article brings together both published and unpublished results from this project, strengthening the trends that had been emerging and bringing new insights into the development of artists’ materials over this period. A notable finding during the programme was the discovery of two paint additives—colourless powdered glass and zinc sulphate (white vitriol)—probably added as driers. The new quantitative analyses of the glass composition presented here add to those already published, and reveal that towards the end of the fifteenth century high lime–low alkali glass begins to be used. This observation holds the potential to contribute to questions about the dating of Netherlandish paintings. A smaller number of occurrences of zinc sulphate were identified suggesting that it was less common than glass as an additive, but it is nevertheless significant since it was used by a key figure in the history of oil painting, Jan van Eyck, and occasionally, where present in excess, has caused conservation problems such as drying defects in the paint. Occurrences of the unusual pigments vivianite and fluorite were identified in a few sixteenth-century works. The main changes encountered during the period, however, were the introduction of the blue pigment smalt, its instability having consequences for the current appearance of the paintings, and of a green copper mineral pigment composed of mainly copper sulphate. The latter has proved to be far more common than had been realised in the past.