Prussian Blue Uncovered: The Colour

Finally, it is time for the most aesthetically pleasing blog post of the Prussian Blue Uncovered series; colour and swatches! This post will talk about the use of the colour in watercolour; how it compares between commercial and handmade brands, mixes it excels in, and viable alternatives, should you decide that you would rather use a different pigment. When I am able to provide pictorial evidence (for example, mixing swatches), I will be as brief as I can be in terms of describing them, so you can make your own conclusions.

Prussian Blue is widely considered a cool blue; it makes vibrant greens, however purples mixed with this colour are slightly more muted. You can see in the colour wheel above however, that it actually very central in the spectrum of blues, more comparable with phthalo blue red shade than the green shade. It’s complement would be a similarly muted yellow-orange, however any orange would be suitable for this.

Fact-file: PB27

Mid blue
Moderately Staining
semi-Transparent
Non-Granulating
Debatable Lightfastness
Large colour shift
Hexcode: #003153

Colour Mixing

The swatches below have been done on Fabriano paper that is 25% cotton; it is highly likely that colours will behave differently on 100% cotton, so I will also talk about that in this blog post.

Yellows

Cool yellows (green leaning) give bright vivid greens, and some beautiful forest shades. Warm (orange biased) yellows on the other hand give more mossy, “natural” hues, that would be great for woodlands or moss.

Reds and Violets

PR255 is the nearest colour in this selection to neutralise prussian blue, and you can see the blue-leaning grey in the selection below. Most of the other colours are not too attractive (at least, for me), however I can see that they would be useful.

PV19 (the middle two images), regardless of whether it is more red or purple leaning, give super vivid purples. They’re pure and stunning. The redder PV19 gives slightly more grungy hues, but I find I like them more than the bright colours.

PV16 (Manganese Violet) was chosen to see how it would act like with a more granulating colour. There isn’t much separation, but some nice soft hues are made.

Greens

This is my favourite combination; I love deep teals and the middle shade here is stuuuuuuuning.

Earth Tones

Yellow Ochre gives some beautiful earthy greens, and a surprisingly nice steel blue, whereas Burnt Umber gives darker greens and some nice moody blues.

Paint Making

Prussian blue, it seems, is either a love-it-or-hate-it kind of pigment to mull. It is quite grainy when you first start, and clumps together readily in spindrels. Whilst it doesn’t require a lot of gum arabic, patience and plenty of mulling is required. This was one of the first pigments I ever mulled… And I wouldn’t recommend it for beginners. Prussian Blue is an exercise in patience, and upper arm strength!

Commercial brands don’t have this issue; large rollers crush the pigment into the binder over prolonged periods of time. Whilst I cannot be 100% sure, because I’ve not analysed the pigment itself, I strongly believe that the smaller particles resulting with this intense grinding would lower the lightfastness of the paint. It is something I will continue to study, and will begin lightfastness tests shortly.

Brand Comparison

As you can see, the chroma varies between brands. It is also noted at handprint.com, that there is varying lightfastness between the brands. As a general rule, if the pigment has white added to it (i.e. in Antwerp blues

In other mediums this effect is less pronounced, however, in watercolour there is nothing to mask what happens to the colour in mass tone and tints. No matter what brand you choose, I would thoroughly recommend that you perform your own lightfastness tests if you intend the piece to be exposed to light for an extended period of time. (link to Lise’s resource)

Alternatives

So; what should one do, if they want to use Prussian Blue, but don’t want to deal with the lightfast issues? After all, we can hardly tell clients to put their art in a cupboard for half a year!!

I would recommend two alternatives to this colour. If you are looking for a dark blue, go for an indanthrone blue, PB60. If you’re wanting to match the hue (but with a lighter value), a phthalo blue red shade (PB15:0, PB15:6) might be your best bet. A mix of those two would make a suitable dupe for general use (see below), and you could mix your own from tube paints. As the two composite pigments are both blues, your resultant mixes will not be muddied.

I hope you all have taken something away from this mini-series, and are looking forward to the next pigment that we uncover together. Please comment below if you have any requests.

Khannah x