Prussian Blue: First synthetic color of the Industrial Revolution, discovered by accident in 1704 while a chemist was trying to formulate artificial crimson. Warm blue with more muted tint than Phthalo Blue. It has a high tinting strength, is lightfast, and is especially beautiful in its transparency.

Pigment: Ferri-ammonium ferrocyanide (PB 27:1)
Vehicle: Alkali refined linseed oil
Lightfastness I, Series 2, SEMI-TRANSPARENT

reference: www.gamblincolors.com