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Blue Watercolor



The range of Blue watercolor pigments stretches from warm Ultramarines containing varying amounts of red, through to cool, yellow influenced Phthalos and Turquoise. In this article we will examine all their different uses.

Somewhere in the middle of all these colors is a pure blue, uninfluenced by either of the other two primaries – a blue containing no red and no yellow.

Cobalt Blue Watercolor

Of all the blue watercolor pigments we use, Cobalt is the closest to a pure primary blue, however it is a weak, transparent pigment and is easily overpowered when mixed with other colors so we need a selection of blues to be able to mix a full range of colors.


Because of Cobalt’s transparency and its non-staining nature, it is ideal for over glazing. It will cool down a background, pushing it way back into the distance. Cobalt Blue watercolor can be built up wash after wash without it filling the paper texture and lifting off like a sedimentary pigment such as French Ultramarine Blue.

comparison between Ultramarine Blue and Cobalt Blue watercolor


The first wash is made up of several layers of French Ultramarine Blue – each applied after the preceding wash dried. The second example shows the same method used with Cobalt Blue. The Ultramarine pigment has filled the papers texture and is starting to go streaky. The Cobalt wash remains flat and even.


Ultramarine Blue Watercolor

Ultramarine Blue is a warm blue containing traces of red. It sits towards Violet on the color wheel. Ultramarine is a strong, sedimentary pigment and mixes well with other colors to make rich strong darks, subtle greys or mauves. It can be used to mix dirty, compound greens, but, because it contains traces of red, it will not mix a strong, saturated green.


French Ultramarine Blue Watercolor

French Ultramarine Blue is more intense than Ultramarine Blue. It is usually more expensive, but lasts much longer, is much better to mix with and, in the long run, is better value than regular Ultramarine.


Phthalo Blue Watercolor

Moving to the yellow influenced blues, Phthalo Blue watercolor is probably the most intense. It is a strong stain and will bleed up through any colors placed over it.


It can be used to mix vibrant, saturated greens or strong darks. Not being sedimentary means Phthalo Blue can be built up gradually by applying a number of pale washes. Winsor Blue (green shade) is very similar. Prussian Blue and Antwerp Blue are also yellow influenced blues but lack the purity and intensity of Phthalo or Winsor.


Many manufacturers now produce a range of Phthalo Blue watercolors including Red Shade, Green Shade and Yellow Shade. Green or Yellow shade is the best choice to fill the cool side of the blue spectrum.

Example of staining power of Phthalo Blue watercolor


The staining power of Phthalo Blue can be seen here. Painted over a line of dry Phthalo are Permanent Rose, Quinacridone Gold, White gouache and Mid Grey gouache. The Phthalo bleeds up, even through the heavy, opaque gouache.



Cerulean Blue Watercolor

Cerulean is similar in color to dilute Phthalo but much less intense. For this reason it is  a safer color for washes but cannot match Phthalo for strong dark mixtures or if you need a color to stain up through other pigments.


Turquoise Watercolor

Turquoise is a handy accent color, but behaves a little like gouache. A similar result can be achieved by mixing Phthalo and Aureolin with some white gouache.

Indigo Watercolor

Indigo was traditionally a plant based dye but, because of its fugitive nature, paint manufactures now produce a similar looking hue using a mixture of more permanent pigments. Most of these Indigos include Phthalo or Indanthrone pigments making them rich and dark, but also causing them to stain. Indigo does wonderful things when white gouache is flooded into it. The intricate, feathery bleeds make unpredictable, interesting skies.

Indigo watercolor reacting with white gouache


There are dozens of different tubes of  blue available. You don’t need all of them but a well chosen selection of warm and cool blues will satisfy all your painting needs. For me, French Ultramarine, Cobalt and Phthalo Blue (Yellow or Green shade) cover most options. Indigo is a great color to use with Burnt Sienna in limited palette paintings or as a wash for dark, dramatic skies, but it’s not a color I use as often as the other three mentioned here.

A Palette of blues from warm to cool. The first three are the ones I use plus, occasionally, Indigo.

Swatches of various Blue watercolors



This sketch shows the transparency of Cobalt Blue washed over the top right hand corner. It creates a cool receding cast over the area without sacrificing any detail. A splash of Cobalt ties the focal point to the background.

Watercolor sketch showing transparency of Cobalt Blue glaze




A wash of Phthalo mixed with a drop of Aureolin make the intense, transparent turquoise in the painting below. The color has been diluted and washed up into the background to give the painting harmony and provide the focal point with maximum color contrast.


The foreground intensity is the result of gradually building up several layers of wash. The reflections were painted after the Phthalo washes dried. The fact that Phthalo stains and bleeds up through whatever you paint over it ties the reflections to the water.




The color temperature of the blues in this painting shift from cool Phthalo in the foreground to warmer Ultramarine based Mauves in the background. This tends to bring the background forward, echoing the unusual visual effect of distant Jacaranda trees.

watercolor painting of buildings showing shift in blue color temperature between Ultramarine and Phthalo Blue

Another blue I wouldn’t be without is Ultramarine Blue Gouache. Its flat opacity and color intensity can’t be matched with blue watercolor pigments. It is ideal for an intense shot of warm blue. The difference between Ultramarine Blue watercolor and Ultramarine Blue Gouache is the inclusion of Calcium Carbonate and extra pigment in the Gouache to make it flat and opaque.

In this painting the dirty greens, greys and blues of the river are based on Phthalo Blue and the warm blue punctuating the skyline is a flat, opaque mixture of Ultramarine Blue Gouache and White Gouache

Flat opaque Blue gouache sky


Author: John Lovett

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