Fig. 4From: Concerns over colour durability in the nineteenth-century industrial revolution: insights from John Ruskin’s teaching collectionTop left: Afternoon in Spring at Neuchâtel (WA.RS.ED.298.a). Top right: macro-XRF maps of copper (blue) and arsenic (red). Bottom: XRD diffractogram of a greenish area, the asterisks indicate peaks from the paper supportBack to article page