Technical Bulletin Volume 14, 1993
Prussian blue was advertised in Berlin, in 1710, as an opaque pigment of excellent covering power, and was in use (on a decorative element) in Berlin by 1712, and in England before 1721. The modern pigment is lightfast, except when mixed with an abundance of white. Fading of Prussian blue used for skies has been observed in Gainsborough and other 18th-century artists, and cross-sections may show a grey appearance in consequence.
The earliest product was made from dried blood, and had a poor reputation for lightfastness. The chemistry of early and modern Prussian blues is discussed. Water solubility of the pigment increases with increasing potassium content, and so has a tendency to fade, though the manufacturing process also affects lightfastness. English-made Prussian blue was said by several non-English authors to be the best, as regards permanence and brilliance, in the earlier 19th century.