Prussian Blue (PB 27) is a cool (green-toned) blue with a classy subtlety. 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.
Experiment Results
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.
ACMI Ratings
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
Lightfastness: All brands I tested listed Prussian Blue as LFI (excellent lightfastness), but this is questionable to me, as my lightfastness tests above 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
In Kim’s book (and mine), this still makes it a fugitive pigment.
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.
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
On the more bluey end, this dark forest green looks similar to the one you get from Prussian Blue and Serpentine (without the granulation). It’s a great deep dark green that reminds me a bit of Perylene Green. 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
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
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
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.
Debi Riley, Prussian Blue PB27 Colour Mixing Ideas
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.
Prussian Blue is also a lovely mixer, making especially lovely greens because of its strong green bias. Mixed greens from Prussian Blue are not acid-bright like those from Phthalo Green, but they’re also not dull like those from Ultramarine Blue; they’re just nice, deep and velvety.
My problem, when finding room for it on my palette, its that it’s not really “best in class” for any of its use cases:
- Phthalo Blue Green Shade or Phthalo Turquoise are brighter, livelier, and more versatile; also they make vivid, lovely greens and mix with Ultramarine for more lovely skies.
- Cerulean is a better light blue, and mixes bright, opaque granulating greens.
- Ultramarine is more granulating and violet-toned for bold purples.
- Indanthrone or Indigo are darker and easier to use for night skies and shadows.
Prussian might be considered “second best” on any of those individual categories. But it’s very good in all of them. It’s not a specialist; it’s a jack of all trades blue. It’s able to go light or dark (unlike Cerulean which can only go light and Indanthrone/Indigo which can really only go dark). It’s able to become green or purple. And while brighter colors like Phthalo Blue may be more versatile, Prussian’s slight inherent mutedness makes it convenient because it’s faster to mix luscious-yet-realistic greens or stormy skies without necessarily having to manually mute it yourself with red/orange/earth tones.
On my palette? After shifting it on and off my palette over and over, I think I’m finally leaning toward “no.” I find Phthalo Turquoise more useful for most of its use cases.
Favorite version: After doing my own tests with multiple brands I find I should have just listened to Kolbie Blume to begin with: it’s Sennelier.