Prussian Blue was created by accident in 1704. It has associations with Frankenstein, is a registered medicine and could have played a fundamental role in the origin of life. Link
For the artist it offers a subtle, wide tonal range with a tantalising range of greens, especially with lemon yellow and raw sienna. Although 300 years on there are many more blues, Prussian Blue still has qualities no other blue can quite manage.
The Prussian Blue I use was made around the 1960's, and is slightly more muted than contemporary Prussian Blues, a feature I've come to enjoy. Prussian Blue is usually only stable in oil and watercolour, not acrylic, vinyl, emulsions and casein, although some manufacturers do make a stable Prussian Blue for acrylics, Matise for instance. The ratio of pigment to binder also varies in translucency and sheen. Creating a pure velvet pure matt finish is not a given.
Most acrylic Prussian blues are made from phthalo blue with a touch of red and sometimes black and are called Prussian Blue Hue. Although these look similar they behave quite differently when mixing showing phthalo tendancies.
Every pure colour has a code relating to a colour's chemistry not just colour like a Pantone swatch, or HSL values. Prussian Blue is PB27 (Pigment, Blue type 27).
Colours also differ across brands and interestingly there are variations within the product code, so the Prussian Blue from LUX has the Colorindex PB 27.77510.
So when mixing colours based on P numbers we are mixing based on the chemistry of the pigments, so translucency, solubility and reaction to pigments and binders.
Above from LUX Kremer
Matise make their own Prussian Blue for their acrylic range and A J Ludlow make a dry pigment as well along with some gorgeous watercolours
Brunswick Blue, a derivation of Prussian Blue
Brunswick blue was one of the first blues I came across, it was a standard blue in the Redaluma catalogue and the go to blue used in our studio. It consists of a mixture of an iron blue with a large amount of barium sulfate and is chemically similar to Prussian Blue
Below. Underpainting. Same canvas different composition.
