Brunswick Blue is a derivation of Prussian Blue
It consists of a mixture of an iron blue with a large amount of barium sulfate and is chemically similar to Prussian Blue created by accident in 1704. It has associations with Frankenstein and Prussian Blue salt could have played a fundamental role in the origin of life. Link
For the artist it offers a subtle yet wide tonal range with a tantalising range of greens, especially with lemon yellow.Although 300 years on there are many more blues, Prussian Blue still has qualities no other blue can quite manage.
Brunswick Blue is slightly less vibrant than Prussian Blue, a feature I've come to enjoy. Both come with problems, its only stable in oil and watercolour, not acrylic, vinyl, emulsions and casein. The ratio of pigment to binder also varies in translucency and sheen. Creating a pure velvet pure matt finish is not a given.
You will rarely find Brunswick Blue and never find Prussian Blue in an acrylic with the exception of Matise. Acrylic Prussian blues are made from phthalo blue with a touch of red and sometimes black and called Prussian Blue Hue.
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
Below. Underpainting. Same canvas different composition.
