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Cobalt and ultramarine blue are two similar shades of blue. I typically use ultramarine blue when I paint, but I’ve also had a tube of cobalt blue kicking around my box of acrylics, so I decided to put the two head-to-head and compare.
I’ve always considered cobalt and ultramarine to be the most classic blue colours on my palette, especially when I compare it to the pthalo blues, which lean heavily to green, on my palette. Both cobalt and ultramarine blue can be great for mixing greens, painting skies, or anywhere that you need a very typical blue colour.
Watch me compare cobalt and ultramarine blue acrylic paints on my YouTube channel.
On this swatch sheet, I mixed both cobalt blue (PB28) and ultramarine blue (PB29) with:
- Two reds – quinacridone magenta and cadmium red
- Two yellows – cadmium yellow medium hue and cadmium lemon
- Burnt sienna
- I also used titanium white to show the undertones of each blue
The comparison
Ultimately, I didn’t find any dramatic differences between the two. The biggest noticeable difference is that ultramarine blue is darker than cobalt blue when used straight from the tube. Ultramarine blue is a touch warmer (redder) than the cobalt blue, but I don’t consider it to be enough to keep investing and using both colours.
When you compare the swatches in the photo above, please note that I didn’t attempt to use the exact same amount of each colour in each mix – I generally aimed to have one mix that leaned more towards blue, and one mix that had more of the mixing colour, so that we could see a bit of a range.
Pricewise, ultramarine blue is close to half the price of a tube of cobalt blue acrylic paint. If you’re looking for a more affordable option, ultramarine blue wins, hands down. Cobalt also has some toxicity issues that I would rather avoid, and ultramarine blue provides an excellent alternative.
Ultramarine blue is my choice
Once I use up the tube of cobalt, I won’t buy it again and will just continue to use ultramarine blue. You may find that you prefer cobalt, or to have both on your palette, or a different brand or shade of cobalt blue might give you different results.
Learn more
Check out a listing of all my colour mixing blog posts and videos on my colour mixing roundup article.
Buy your own
Pick up some paint at your local art supply store or on Amazon:
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