Colour changes due to the fading of Prussian blue in Danish Golden Age paintings

Examination of oil paintings by artists from the so-called Danish Golden Age in the first half of the nineteenth century indicates that a significant degree of deterioration and fading has occurred in a number of cases in some of the blue coloured areas. The occurrence was initially suggested by the different appearance of the paint along the edges of the paintings where they had been protected from the light. Technical examination of paintings from the Statens Museum for Kunst collection, by artists such as Christen Købke, Nicolai Abildgaard and C.W. Eckersberg, revealed the presence of Prussian blue, mixed with lead white and calcium carbonate as a component of the paint in the affected areas. Due to its high tinting strength, Prussian blue was often used – mostly in moderate proportions - mixed with other compounds and pigments. It has been demonstrated by experimental studies that the durability of the colour changes dramatically when the pigment is mixed with certain whites. Among its virtues, the relatively modest price would seem to account for its frequent occurrence in Danish paintings from the mid-18th century onwards, though reservations about the permanence of the pigment are found in several written sources already a few decades after its first appearance on the market. It is therefore doubtful whether this awareness or the scepticism voiced in the literature was to any extent shared by 19th-century users of the pigment, or whether Danish suppliers of the period were in general concerned with the exact nature of their product.
The recent technical examination has caused an art historical reappraisal of some of the works from the era. In a broader sense, the research, combining scientific analysis, archival, and art historical studies has led to the realization that paintings of the Danish Golden Age were in some cases created with brighter, more contrasting and striking colours than the rather subdued and harmonious tonality with which these paintings are often associated by present-day viewers.