Pigment Blue 27 (PB27) is famous for being among the first modern synthetic pigments ever created, Prussian blue was discovered by chance in 1704 by the Berlin-based colourmaker Johann Jacob Diesbach. This accidental discovery provided a new alternative to the only permanent blue pigment available, ultramarine (lapiz lazuli), which was extortionately expensive as it was mined in limited amounts in Afghanistan.
It spread through Europe in watercolour and oil colour, with artists such as Antoine Watteau and Jean-Baptiste Pater taking it up. It then travelled globally, as far as Japan, where it was used by Hokusai in his woodblock painting The Great Wave off Kanagawa. Since then, Prussian blue has featured in the palettes of artists including Monet, Constable, Gainsborough, Lowry and Picasso in his famous “Blue Period”.
Even though it is suitable for oil and watercolour binders, Prussian Blue has a rather bad reputation. It became clear soon after its invention that it was unstable and prone to fading when exposed to light or mixed with certain alkaline pigments. Across the following centuries many different manufacturers were making the pigment, and not always to the best standards, so when Phthalocyanine pigments were introduced in the middle of the 20th century many artists were relieved to leave behind the potentially troublesome Prussian Blue in favour for the reliably lightfast Phthalo Blue.
Several independent tests carried out by artists show that there is considerable variation in lightfastness. Bruce MacEvoy of Handprint tested a range of Prussian Blue watercolours and found that some faded slightly, some substantially, and some hardly changed at all. What is certainly clear is that Prussian Blue is more prone to fading when mixed with a white pigment. According to a study by the National Gallery, London, this is because the addition of white increases the reflection of light within the paint layer. Interestingly, Prussian Blue paint that has faded recovers its colour after being stored temporarily in a dark space with good airflow. There have been many studies that show this is the case, and some museums rotate their displayed collections to ensure that works containing Prussian Blue have some time to recuperate.
iron blue lightfastness samples (2004)
after 800+ hours of sunlight exposure
(top, left to
right) Utrecht, M. Graham, Rembrandt, Schmincke, Holbein,
MaimeriBlu; (bottom, left to right) Rowney Artists, DaVinci, Van
Gogh, Daniel Smith, Winsor & Newton, Winsor & Newton antwerp blue.