Made from the heavy metal cobalt, this is a true neutral blue that’s neither green-toned nor purple-toned, and is a perfect shade for clear blue skies.
Experiment Results
Gradient: Grades from a bright blue to a pale sky blue. Not dark in masstone.
Opacity: Slight dust on the black line. I would call this semi-transparent.
Glazing: Glazes to a nice royal blue.
Colors Mixes: Well-behaved in mixes, turning my transparent rainbow into several nice, bright, clean, granulating shades of purple and green. Neutralizes oranges to brown.
Lifting: A nice easy lift both wet and dry. I got a really lovely cloud shape on the wet paint with a dry paper towel, and I also was able to scrub to a bright white on the dry paint with a wet paper towel. This “cloud-ability” reinforces Cobalt Blue as a great sky color!
Comparison to Other Colors
Ultramarine (PB29) & Cobalt Deep (PB74)
Cobalt Blue and Ultramarine Blue (PB29) are both highly granulating, medium-tinting blues. Roughly, Cobalt Blue tends to more of a middle blue while Ultramarine tends to be more of a purple-toned blue. However, both come in various slightly different tones (more greenish or more reddish) and different levels of granulation depending on the brand and style, and there can be some overlap in the categories.
In addition, there is another pigment called Cobalt Blue Deep (PB74) which is similar to Ultramarine in that it is highly granulating and purple-toned.
Here’s a big comparison of several I’ve tried:
Across brands, I found that Cobalt Blue (PB28) is generally always less purple-toned than Ultramarine Blue (PB29), but “light” or “green shade” Ultramarines are pretty close in hue – I can tell the difference, but I probably wouldn’t want both on my palette.
I also found that Cobalt Blue Deep (PB74) held its own among French Ultramarines for level of granulation and purple tone.
Personally, I like to have colors at both ends of this spectrum (a Cobalt and a French Ultramarine), but I think if you only want one, a light or middle Ultramarine will get the job done. Or whichever one you like best – Cobalt and Ultramarine are colors that mix similarly and can be substituted for each other.
Careful of Hues!
Some brands offer colors called “Cobalt Hue” or similar that are not really PB28, but a mix of other blues. For example, Mission Gold’s Cobalt Hue No. 1 is a mix of Ultramarine and Phthalo Blue.
Comparison to Other Brands
Most brands offer a PB28 Cobalt Blue, and they are mostly called Cobalt Blue. Some companies use the term ‘Cobalt Blue’ for hues made with Phthalo Blue (PB15), so be careful and look at the pigment number.
Daniel Smith – Cobalt Blue
Daniel Smith’s Cobalt Blue was the first one I tried, and it made me think, “I don’t like Cobalt Blue.” It’s hard and difficult to rewet with a low tinting strength; I struggled to get deep color out of it. It is also very granulating in a way that I found incompatible with skies.
Holbein – Cobalt Blue
A deep, rich blue. This paint is very easy to rewet and get nice and pigmented. More granulating than Da Vinci, though less wildly so than Daniel Smith.
I think Holbein’s Cobalt is very beautiful and balances texture and handling extremely nicely. It does have more texture than I normally like in a sky, but it’s pretty to look at even if it doesn’t have real-life verisimilitude.
Palette Appearance
Looks wonderful on the palette. You will never mistake it for anything else.
Color Mixes
Lemon Yellow (PY175)
Distinguishes itself from the Ultramarine mix with yellow by actually making green. These are reasonably bright, clean greens, not as neon-bright as the ones you’d get from Phthalo Blue or Cobalt Turquoise. Floating blue granulation in dilute.
Monte Amiata Natural Sienna
Non-green mixes of gray-blue to gray-tan.
Yellow Orange
I’m not a fan of the muddy orange-grays I got from the mix, though I like the way the yellow-orange darkens the blue to a navy night sky color when the mix is mostly blue.
Transparent Pyrrol Orange
A range of browns, grays, and gray-blues from a warm terra cotta/clay soil color, through to cool brown, balanced gray, and stormy gray-blue as you add more of the Cobalt to the orange. In dilute, you can see more of the granulation with the blue floating above the orange. Similar to mixes of Ultramarine and TPO.
Transparent Red Oxide
More reddish and subdued range of browns and grays than from the Transparent Pyrrol Orange. I really like the bright, medium browns and granulating diluted mixes. Similar to mixes of Ultramarine and TRO.
Perylene Maroon
Another range of browns and blue-grays, but compared to TRO, these are much redder browns and purpler blue-grays. I really like all of these.
Quinacridone Rose
A nice range of bold purples; more periwinkle when tilted toward Cobalt, through lavender and lilac to a more cool magenta shade than the (relatively warm) Quin Rose variant Red Rose Deep. The more bluey and watery mixes have clear granulation with blue granules floating over the pale pink/purple background. Slightly less intense than mixes with Quin Rose and Ultramarine.
Quin Magenta (PR122)
Very bold intense purples! These are some of my favorite purples ever.
Potter’s Pink
The Potter’s Pink floats above the Cobalt, creating interesting separated mixes that have a far-away appearance of muted lavender.
Cobalt Turquoise
Look at this sky power couple! To me, if you flip that gradient 90 degrees so that Cobalt Blue is on top and Turquoise is on the bottom, it looks just like a clear blue sky. Cobalt Turquoise is perhaps a shade too green for a horizon sky, but you’ll have to allow for poetic exaggeration. The diluted mix of the two colors looks just like I always expect Cerulean to look (but actual Cerulean is duller).
Viridian
Pleasant granulating turquoise colors, darker than Cobalt Turquoise, bolder than Cobalt Turquoise Deep, and less neon than Phthalo Blue + yellow mixes. Granulation adds to the appearance of light in water.
What Others Say
Cobalt – I reached for cobalt [in the Petrified Forest] when I wanted a blue that would stand on it’s own more, as it is a much less vibrant color at lower concentrations compared to ultramarine, and also leans more toward green than purple which is what I often wanted for the blue colors of the petrified wood. In mixtures, cobalt is a bit harder to use because it just takes so much more paint to get it to be the dominant color.
Claire Giordano, Petrified Forest Residency: Favorite Colors
My Review of Cobalt Blue
Cobalt generally has less value range than most of my favorite blues (you can’t make a night sky with it), but in my opinion, nothing comes as close to matching the color of a clear blue sky! (Yes – I prefer diluted Cobalt Blue to any Cerulean.) It also allows for lovely lifted clouds.
In mixes, it behaves similarly to Ultramarine, but more versatile: it cheerfully mixes both greens and purples, as well as browns and grays with orange. Floating granulation adds interest to any mix.
Cobalt Blue can handle the work of being a ‘primary blue’ on a limited palette, and also has value as a blue-sky specialist on a more expansive palette.
On my palette? Yes!
Favorite version: Da Vinci – after playing around with different levels of granulation I like this one the best for skies and mixes. The more I use it, the more I like it!