Color Spotlight: Cobalt Blue (PB28)

Da Vinci Cobalt Blue: gradient, opacity and glazing, color mixes

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 tests: Wet Paint/Dry Paper Towel vs Dry Paint/Wet Paper Towel

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:

From left: Da Vinci Cobalt Blue (PB28); Holbein Ultramarine Light (PB29); Da Vinci Ultramarine Blue (PB29); Winsor & Newton Cobalt Blue Deep (PB74); Da Vinci French Ultramarine Red Shade (PB29)

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.

Mission Gold – Cobalt Hue No. 1 (PB29, PB15:3)

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 – 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

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.

Cobalt Blue comparison, from most to least granulation. From left: Daniel Smith, Holbein, Da Vinci. (In this photo, Holbein looks more red-toned, but they’re actually about the same hue.)

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.

Shimmery Palm – day 9 of Kolbie Blume’s “Painting the Wilderness: Seascapes” challenge. May 2022. The sky is made from Holbein Cobalt Blue.

Palette Appearance

Looks wonderful on the palette. You will never mistake it for anything else.

A bright jewel of newly filled bright blue Cobalt in the middle of my palette.

Color Mixes

Lemon Yellow (PY175)

Winsor Lemon + DV Cobalt Blue

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.

Naples Yellow Deep (PBr24)

DV Cobalt Blue (PB28) + WN Naples Yellow Deep (PBr24) on Wonder Forest

Muted, soupy greens in the middle.

Monte Amiata Natural Sienna (PBr7)

DV Cobalt Blue (PB28) + DS Monte Amiata Natural Sienna MANS (PBr7) on Wonder Forest

Non-green mixes of gray-blue to gray-tan. Gray has a hint of green.

Raw Sienna (PBr7)

DV Cobalt Blue (PB28) + DV Raw Sienna (PBr7) on Wonder Forest

Redder than MANS and not at all green. Makes cool tans.

Isoindolinone Yellow (PY110)

Holbein Isoindolinone Yellow Deep (PY110) + DV Cobalt Blue

I’m not a fan of the muddy tans I got from the mix (the Raw Sienna/earths make much nicer browns), though I like the way the yellow-orange darkens the blue to a navy night sky color when the mix is mostly blue.

Benzimida Orange (PO62)

DV Cobalt Blue (PB28) + DV Benzimida Orange (PO62) on Wonder Forest

Strikingly evenly gray in the middle! A light gray with some interesting, subtle color separation. The more orangey mixes are pretty ugly – again, earths are nicer on this side.

Transparent Pyrrol Orange (PO71)

DS Transparent Pyrrol Orange (PO71) + DV Cobalt Blue

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.

Quinacridone Burnt Orange (PO48)

DV Cobalt Blue (PB28) + DS Quinacridone Burtn Orange (PO48) on Wonder Forest

Granulating browns and grays; none get too dark.

Transparent Red Oxide (PR101)

Transparent Red Oxide + Cobalt Blue
DS Transparent Red Oxide (PR101) + DV Cobalt Blue – in Wonder Forest sketchbook

I really like the bright, medium browns and granulating diluted mixes. These mixes can get quite dark. Similar to mixes of Ultramarine and TRO.

Perylene Maroon (PR179)

Perylene Maroon + Cobalt Blue
Daler Rowney Perylene Maroon (PR179) + Da Vinci Cobalt Blue (PB28) on Wonder Forest paper

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.

Deep Scarlet (PR175)

DV Cobalt Blue (PB28) + DS Deep Scarlet (PR175) on Strathmoor Cold Press

Distinctly violet, though somewhat muted.

Naphthol Scarlet (PR188)

DV Cobalt Blue (PB28) + DV Permanent Red (PR188) on Wonder Forest

Similar to Deep Scarlet mixes, especially on the blue end. The more PR188 side looks muddy to me.

Quinacridone Rose (PV19)

DV Cobalt Blue + Da Vinci Red Rose Deep (PV19)

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)

DV Cobalt Blue (PB28) + Holbein Quin Magenta (PR122) on Canson XL

Very bold intense purples! These are some of my favorite purples ever.

Potter’s Pink (PR233)

MaimeriBlu Potter’s Pink (PR233) + DV Cobalt Blue

The Potter’s Pink floats above the Cobalt, creating interesting separated mixes that have a far-away appearance of muted lavender.

Cobalt Turquoise (PG50)

Cobalt Turquoise + Cobalt Blue
SH Cobalt Turquoise (PG50) + DV Cobalt Blue (PB28) on Arches

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 (PG18)

DV Cobalt Blue + Winsor & Newton Viridian (PG18)

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 its 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, [Daniel Smith Cobalt Blue] 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

Cobalt blue is today often displaced from the palette by ultramarine blue (PB29) or phthalo blue (PB15), which have very different textural and handling characteristics but are less expensive. The color and texture can be approximated by ultramarine (PB29) mixed with a small amount of phthalo blue (PB15:3). But pure cobalt blue is unique: versatile in mixtures with a beautiful color that will endure forever, even in the thinnest wash, and a natural texture that accents the finish of any fine paper.

Bruce MacEvoy, handprint.com (2010)

Cobalt pb28 is my staple blue that is first on my list to get. Especially for beginners watercolour painting. It mixes beautifully with just about everything I throw at it, creating a lovely range of foliage greens, browns, greys, mauves.  Cobalt pb28 is a clean, Transparent blue paint colour that is great for glazes. This artist quality blue paint is the perfect blue for a sunny blue sky day. Used for foliage, ocean, sky, hills, trees, still life, just about everything.. Brilliant!

Debi Riley, Dive Into the Mysteries of Blue Paint (2015)

My Review of Cobalt Blue (PB28)

Cobalt Blue generally has less value range than most of my favorite blues (you can’t make a night sky with it), but it’s my favorite daytime sky specialist. In my opinion, nothing comes as close to matching the color of a clear blue sky. I prefer its slightly violet-toned, candy-blue hue to the greener sky classic Cerulean Blue.

Nature Spot 2024 – Jan 22. Blue sky with Cobalt Blue and Phthalo Blue Red Shade.

It also makes unbeatable cloud shadow mixes, lightly color separating and intense.

Single clouds from Maria Coryell-Martin’s Cloudscapes class. June 13, 2022. Cobalt Blue, Quin Violet, MANS, Cobalt Turquoise.

In mixes, it behaves similarly to Ultramarine Blue, making browns and grays with oranges and earth oranges, though it has less range and doesn’t get as dark. It can mix serviceable middle greens with yellow, but the purples are my favorite purples: ethereal mixes, better even (in my opinion) than those with more violet blues.

In this desert canyon practice piece from November 8, 2022, the twilight sky is a combo of Cobalt Blue and Red Rose Deep.

I also find Cobalt Blue especially useful for atmopsheric perspective: swapping darker shadows for midtone Cobalt Blue can make a mountain look hazy and distant.

Cape Breton National Park. February 8, 2024.

Unfortunately, even more so than other Cobalt colors, Cobalt Blue is toxic and expensive. If it’s too expensive for you or you’re making a nontoxic palette, I like Phthalo Blue Red Shade for a sky color alternative and Ultramarine Blue for cloud shadows and other mixes. (Ultramarine Green Shade is closest to Cobalt Blue hue; though a mix of regular Ultramarine with a bit of a Phthalo can also work.) With these colors, Cobalt Blue is unnecessary, though I still quite like it. It has a certain je ne sais quoi.

On my palette? Yes!

Favorite version: Da Vinci – after playing around with different levels of granulation I like this low-granulating, ultra-bold one the best.

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