Figure 9
Color change observed after 400 h light exposure in commercial and eighteenth-century Prussian blue pigments painted from gum arabic in both dark and light shades. The blue points correspond to commercial Prussian blue painted in dark shade (solid points) and light shade (open points), and the red symbols correspond to eighteenth-century Prussian blues, painted in dark shade (solid symbols) and light shade (open symbols). Δa* corresponds to the transition from green to red, shown at the top, and Δb* corresponds to the transition from blue to yellow, shown at the right. The values inside the oval are for LPA2, D2 and D3, all of which contain ferrihydrite. |