Color Spotlight: Prussian Blue (PB27)

Prussian Blue (PB27) is a dark blue with a cyan tone. On a scale of Moody Emo Teen (Indanthrone Blue) to Manic Pixie Dream Girl (Phthalo Blue Green Shade), I would put Prussian Blue somewhere in the middle.

Pigment Stats for PB27

Chemical composition: ferric ferrocyanide (derived from iron)

Invention year: 1706, making it the oldest “modern” synthetic pigment. (Older synthetic pigments were created in ancient world, such as Egyptian Blue or Mayan Blue.)

Lightfastness: All brands I tested listed Prussian Blue as LFI (excellent lightfastness), but this is questionable to me, as my lightfastness test showed dramatic fading. However, it’s evidently possible for Prussian Blue to fade and then recover. Per Kim Crick:

Prussian Blue pigment has a chemical reaction to UV light exposure. It is different than the standard fading that happens in other pigments. This is caused by the oxidation of ferrous ferrocyanide salts. Sun bleaches the FeIII (Iron) which requires time to re-oxidize away from light. Because it is possible to regain color intensity over time in shade, manufacturers have lazily marked it as LFI.

Kim Crick, Fugitive Pigments List

I would still call this a fugitive pigment as it is not reliable for display in a sunny area.

Toxicity: AP (non-toxic). Bruce MacEvoy notes,

PB27 is completely nontoxic and nonpolluting; it has even been used as an oral antidote to heavy metal poisoning and as a soil treatment (to increase iron) in agriculture. It can produce cyanide gas if heated or burned, and it has been known to ignite during grinding.

Bruce MacEvoy, handprint.com

Observations of DS Prussian Blue

Graded Wash: I was pleased with how dark I was able to get this. My favorite kind of Prussian Blue is dark Prussian Blue, the perfect night-sky color. In dilute, it could also be used for clear daytime skies.

Opacity/Glazing: Extremely transparent. The glaze is super dark.

Mixes: Generally pleasant if somewhat muted range of purples and greens. The mixes with yellow/gold make nice, gently granulating realistic landscape greens, which is always something I find difficult to do with actual greens. But my personal favorites are the mix with Phthalo Green Blue Shade, which ends up resembling Phthalo Turquoise Blue, and the mix with Quin Purple, which ends up looking a bit like Indanthrone Blue.

Lifting: Because this is a blue sky color, I did a lifting experiment (using Da Vinci Prussian Blue). On the left, I used a dry balled-up paper towel to lift a cloud out of wet paint. On the right, I left the paint dry and then used a wet balled-up paper towel to scrub out a cloud. In this paint, I prefer the dry paint lift, which I was able to scrub really white (the the wet-paint lift left behind some blue spots in the cloud, which don’t look terrible – sort of like shadow).

Lightfastness

I tested Holbein’s Prussian Blue and found that over 6 months in a sunny window, it significantly lightened and became greener-toned.

Comparison to Other Brands

Most companies offer a Prussian Blue. Some companies make more than one shade with PB27; for example, Winsor & Newton makes both Prussian Blue and Antwerp Blue (PB27). As far as I can tell, this is a version of Prussian Blue that gets less dark.

Here are some I’ve tried.

Da Vinci Prussian Blue

Da Vinci’s Prussian Blue is very similar in color to DS, but a bit brighter and greener.

It’s easy to get super-dark, easy to grade smoothly, and makes lovely green mixes. (Ignore the fact that I didn’t do the glazing test right, I had run out of paint on my palette.)

I think this is going to my go-to Prussian Blue going forward; being extra-dark and extra-green-toned are assets for me because I use it for night skies and mixing greens. You might want to pick another one if you prefer a neutral mid-tone blue.

Holbein Prussian Blue

Color-wise, Holbein and Daniel Smith look just the same to me. I found Holbein’s more difficult to grade prettily, but that could be a fluke. The mixes were easy and pretty, and I especially like its color in dilute for the sky.

Multiple Brands

Here are some more swatches of Prussian Blue that I tried in subsequent months. I arranged these roughly from least to most bright… but it’s subtle; they’re extremely similar.

All of these were painted from dry dots. I found Mission Gold the overall dullest, DV is fine, Schmincke is low tinting strength. Sennelier was my favorite, lending itself well to a deep masstone and the most bright cyan dilutes (you could almost use it as a sky color), but it was only marginally different from the others.

Comparison to Other Colors

Phthalo Blue & Turquoise

Prussian Blue has a similar green-leaning cyan blue hue to Phthalo Blue Green Shade (PB15:3), but Prussian is noticeably darker and more muted.

I find Phthalo Turquoise (PB16) to be a reasonable swap-in for Prussian Blue because it also makes wonderful greens. The WN version is also on the muted side, and gets very dark, however other brands don’t necessarily have these quality.

Prussian Green

Prussian Green is a color name offered by several brands; it is usually a commercial mix of Prussian Blue plus some green or yellow, to make a greener hue, but the Schmincke version pictured above is actually a mix of Indanthrone Blue and Phthalo Green to make a Prussian-like muted green-blue hue without any actual Prussian Blue pigment.

Color Mixes

Winsor Yellow

These cool greens are nice, but to me they fall into the awkward middle zone between super-bright (as Winsor Yellow + Phthalo Blue) and super-muted (as Quin Gold + Ultramarine). Still, they’re not bad options for greens that may look bright or muted depending on surrounding context.

Rich Green Gold

Gorgeous dark forest greens on the more Prussian Blue side. Wow, I love that. Perfect for pines! As you move toward the Rich Green Gold end of the spectrum, it becomes more of a an avocado yellow-green.

Nickel Azo Yellow

A broad variety of wide-ranging greens including a glowing teal, an awesome foliage/pine green, and a variety of yellow greens and green-golds.

Pretty similar to the Rich Green Gold mixes, but with a bit more variety in the yellow range. It’s a bit easier to make cool greens from RGG and warm greens from NAY. But they’re extremely similar, and there’s a ton of overlap in the greens you can make.

Gently muted bluestone and undersea green type mixes.

Transparent Brown Oxide

A nice range of rich browns! I also like the dark muted teal.

Quin Burnt Orange

Quite a wide range of blues/greens/browns here. This is not quite a complementary pair, they’re both yellowish so the middle is more of a green than a gray.

Transparent Pyrrol Orange

This is closer to a complementary pair since TPO is redder-toned than QBO. Still, it doesn’t quite get to gray, the most neutral mix being a dark loden. This mix also makes a pretty nice range of cool browns similar to Raw Umber.

Quin Burnt Scarlet

This is also close to a complementary pair, though a bit more on the red side, making a dark red-brown instead of a black/gray. On the more blue side, QBS is a nice muting agent to make the Prussian Blue into a moody blue-gray.

Deep Scarlet

Huh! Judging by the pure unmixed hue, I would have said that Deep Scarlet is less orange than Quin Burnt Scarlet, but I had an easier time making what looks like a black/gray color rather than a purple with Prussian Blue. I really like black color as well as the dark, muted navy with mostly Prussian Blue. These are nice! I prefer them to the QBS mixes.

Perylene Violet

You can get really dark colors from this because both the mixers are dark, but you’ll see the tint of the mix as you dilute it – a range of blue-grays and purple-grays.

Alizarin Crimson Quinacridone

The middle muted purples are not really interesting to me, but I really like the more blue end (violet blue) and the more red end (dark burgundy).

Cerulean

Prussian Blue deepens the Cerulean within the same hue range.

Serpentine

This was a surprise hit! I love these deep, dark granulating cool greens.

What Others Say

A strong, dark, cold blue. I use this if I want a really dark colour. Combined with Indian red or burnt umber, it gives a colour approaching black. It has a high staining quality.

Richard Bolton, Handbook of Watercolour Landscape Tips & Techniques (2009)

PB27 can achieve a beautifully saturated, very dark color in some preparations, but when used in watercolors its finished color is usually muted, greenish and moody… The ASTM (1999) rates the lightfastness of PB27 in watercolors as “excellent” (I), but my lightfastness tests showed that this pigment is unusually variable both within and across brands. 

Bruce MacEvoy, handprint.com (2010)

Fugitive pigment often mislabeled as lightfast in watercolors. Unfortunately PB27 always fades in sun, but might recover in shade. Manufacturers who are aware of the issue may mark it as lightfast due to it’s ability to regain color after being removed from light. In my opinion, paint should not need to be taken off the wall for a nap in a dark corner for it to be considered lightfast. I avoid this pigment if planning to sell a painting or display it in a gallery, because a buyer is likely to hang it in a room with a window. It is only stable in indoor artificial light or museum low-light conditions.

Kim Crick, Blue Swatches

Not one of my favourites, Prussian Blue is an alternative [to Phthalo Blue] if a less staining cool blue is desired. Made from PB27. Easily mixed with Phthalo Blue and a warm red.

Jane Blundell, Watercolor Comparison: Blues

Note that I personally did not find Prussian Blue to be “less staining.” Rather I agree with Richard Bolton that is “high staining.”

Prussian blue is a deep and mysterious blue paint that creates the most magnificent foliage greenery. I love its tonal ranges from a very dilute pale cool greeny blue to the full mass tone of near midnight blue black… Mixed with winsor lemon creates nice spring yellow greens; mixed with burnt umber – a darker cooler forest pine green.  Sometimes I will add a slash of it into my ocean waters, to provide a hint of deep dark greeny blue to draw the eye.

Debi Riley, Prussian Blue PB27 Colour Mixing Ideas (2015)

My Overall Thoughts

I really like the color of Prussian Blue. I love it especially in mass for dark night skies. I fell in love with it after one of my very first watercolor classes, a Night Sky tutorial with Shelby Thayne.

I love the mixes you can easily get from Prussian Blue, including the grays and browns, but especially the greens. I love the greens. They are deep and lush, never muddy nor garish. It’s just Green Perfection.

Brighter colors like Phthalo Blue are more versatile; they can mix brights that Prussian can’t. But Prussian is more convenient for situations where a little mutedness is called for, such as deep greens, dusk skies, cloud grays, etc.

I am disappointed in the lightfastness tests. That’s a fact. I still enjoy Prussian Blue for noodling around, but for lightfast artwork, my preferred mixer for deep greens is Phthalo Turquoise (PB16), and my preferred dark blue is Indanthrone or Indigo.

Favorite version: Because this tends to be a sticky pigment even in not-typically-sticky brands (such as DS), and I can’t abide stickiness, my favorite is WN. The stickiness inherent in the pigment balances WN’s tendency to dry rock hard.

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Winsor & Newton – Prussian Blue, 5 ml Tube: Jackson’s US