Colour Number: 24
Pigment Details: Iron (II, III) Hexacyanoferrate (II, III) / Colour Index Pigment Blue 27 (C.I. PB27)
Prussian Blue Professional Watercolour is prepared using the metal complex pigment, iron hexacyanoferrate, where the iron is present in the complex as a mixed valency ion; iron (II) and iron (III). The pigment has been selected for its purity and hence light fastness, intense blue (green shade) hue, making it ideal for use in A J Ludlow’s Professional watercolour range.
Synthesised by accident in Berlin around 1706 by the colourman Diesbach, the pigment was originally named Preußisch blau (Prussian blue) and Berlinisch blau (Berlin blue), the pigment is also known as Paris blue, Milori blue and the more greener shades, Chinese blue.
The deep intensity of the colour, which at full strength is almost black, has led to the addition of white pigments in order to lighten the intensity of the colour. According to Ralph Mayer, the pigment Antwerp blue is a pale variant of Prussian blue made by reducing the iron hexacyanoferrate with 75% of an inert pigment, usually alumina hydrate (which sometimes contains zinc salts). A recent study has found that alumina hydrate and ferrihydrite, often found as impurities in pigment prepared by the early manufacturing processes, also reduce the pigment’s light fastness. The presence of ferrihydrite, which is yellow, leads to a greener shade Prussian blue and alumina hydrate is often used as an inert filler in student quality watercolours due to its acceptable transparency in gum Arabic solutions.
A J Ludlow’s Prussian Blue Professional Watercolour contains only the pigment and no inert fillers. In order to reduce the colour’s intensity, it is best to use dilute washes and so use the whiteness of the watercolour paper to reduce the intense blue. Mixing the Prussian Blue Professional watercolour with A J Ludlow’s Binder and Painting Medium will also reduce the colour’s intensity and still maintain the qualities of a Professional watercolour.
Mayer, R “The Artist’s Handbook of Materials and Techniques”, 5th Ed, Viking, New York, 1991.
Grandjean, F., Samain, L., Long, G.J., Dalton Trans., 2016, 45, 18018
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