Painting a Monochrome with a Family of Cobalt Colours

Artist Ale Casanova challenged the idea of monochrome painting by working exclusively with the Rembrandt cobalt family. Using four cobalt colours and Titanium White, he explored how temperature, transparency and value can create surprisingly rich paintings without ever leaving a single colour family.

Before painting: really looking at the colours

Before deciding which colours I would use in the painting, I wanted to test all of them. I first looked at each colour in mass tone, directly against white, and then extended part of the paint by diluting it with turpentine. I wanted to see the concentrated colour first, and then observe what happened as the paint film became thinner and allowed more of the support to show through.

First test of the seven colours. Each one is shown first in mass tone and then diluted with turpentine, making its transparent or semi-transparent character much more apparent as the paint film becomes thinner.

What Titanium White reveals

I then carried out a second test, progressively tinting each colour with Titanium White.

This second test was particularly revealing. In mass tone these colours have considerable depth, and some can appear much more opaque than they actually feel when used in a painting. Once extended, their transparency becomes more apparent and, when mixed with Titanium White, their true chromatic character is much easier to see. 512 reveals its cooler nature, 515 shifts noticeably towards violet, while 586 opens the palette towards turquoise and green. The 539 takes that progression directly into violet. The family suddenly becomes much broader than it appears when simply looking at the tubes.

The seven colours progressively mixed with Titanium White. Adding white reveals nuances and chromatic shifts that are much less obvious when the colours are viewed directly in mass tone.

Building a restricted palette

I did not want to use every colour available. Instead, I wanted to construct a restricted palette that would allow me to move in different directions while remaining within the cobalt family. I needed a cool blue and a warm blue, one colour capable of pushing mixtures towards green, and another that could take them towards the violet or magenta end of the spectrum. I eventually chose four.

512 Cobalt Blue (Ultramarine) would be my cool blue. It is also a particular case within this selection because it is not a genuine cobalt pigment, but rather a formulation made from other pigments designed to occupy a similar chromatic space. This kind of formulation is common in artists' materials: a colour can be reproduced using another pigment or a combination of pigments in order to reduce the cost of an especially expensive pigment, replace materials that have disappeared or become difficult to obtain, avoid toxicity issues, improve permanence or achieve particular handling properties. In the case of genuine cobalt pigments, cost is certainly relevant: they are exceptionally stable and lightfast pigments, but they are also expensive.

Opposite it, I chose 515 Cobalt Blue Deep, warmer, deeper and more violet in character. Between 512 and 515 I already had my first temperature contrast without even leaving the blues. 586 Cobalt Turquoise Blue allowed me to move certain mixtures towards green and extend that side of the palette, while 539 Cobalt Violet would act as a warm colour, almost performing the role that magenta might have in a conventional palette. I did not need to use it constantly; its purpose was to push certain areas of the painting towards a warmer, more violet extreme.

Four colours and Titanium White.

A little history

Cobalt has been providing colour for far longer than modern oil paint has existed. Minerals containing cobalt were used for centuries to colour glass and ceramics, and smalt, a cobalt-coloured blue glass that was then ground into a powder, was also used as a painting pigment. Modern cobalt blue appeared at the beginning of the nineteenth century, when the French chemist Louis Jacques Thénard developed a stable blue from cobalt and aluminium compounds; other cobalt-based pigments followed, including greens, violets, turquoises and additional blues.

The fact that they all belong to the cobalt family does not mean they are the same pigment. Changing the elements with which cobalt is combined alters its structure and also its behaviour: the hue changes, as do the transparency, temperature and the way the colour reacts when mixed with others. That is exactly what the initial tests reveal: under a common name, we find colours that behave very differently from one another.

Method: starting with the darks

I worked on canvas mounted onto a 30 × 42 cm panel. The first stage was painted alla prima, beginning with the deepest darks using 512, the cooler of the two principal blues. At this point there is no white involved: I work directly with the colour in mass tone and with direct brushstrokes.

At this stage, one characteristic began to influence the entire painting. I found these colours more transparent than I had expected and, as the brushstroke loses body, the support continues to show through. This is especially noticeable in the darks, where I need to retain the colour in mass tone and cannot rely on white to increase opacity. It took a little getting used to, although I did not want to fight against it too much. In some areas I allowed those small transparent passages to remain within the brushwork. The canvas continues to appear between the darker strokes, creating differences in density that I wanted to preserve later in the painting.

First stage of the painting. The deepest darks are built with Cobalt Blue (Ultramarine) 512, without Titanium White.

Moving into the middle values

From those first darks I began introducing 515 Cobalt Blue Deep, our warm blue, followed progressively by Titanium White as I moved into the middle values. The opposition between the two blues therefore begins to appear very early in the process: 512 maintains the cooler end of the range while 515 introduces a warmer, more violet shift.

The behaviour changes immediately once white is introduced. White does not only raise the value; it also gives the paint more body, considerably increases its covering power and reveals much more clearly what I had already observed in the preliminary tests. I work these middle values with direct brushwork, mainly using placed, deliberate strokes: I put the paint down and try not to keep going back over it. In certain areas I may blend two passages slightly, but I try to avoid repeatedly rubbing and overworking the surface until everything turns into a uniform mixture. The darks remain underneath, the middle values sit on top of them and then the lights follow. It is a traditional construction carried out alla prima.

Building the darker middle values. Cobalt Blue Deep 515, warmer and more violet in character, is introduced into the cool 512 base, followed progressively by Titanium White as the painting moves towards the middle values.

Temperature within blue

As I moved upwards through the middle values and into the lights, the other colours began to enter the painting. 586 Cobalt Turquoise Blue allowed me to push certain areas towards green, while 539 Cobalt Violet appears more selectively, acting as one of the warmer extremes of the palette and shifting particular areas towards violet.

One of the things I most wanted to test was how much contrast I could achieve without leaving this colour family, not only contrast between light and dark, but also temperature contrast. Within such a restricted palette, warm and cool are necessarily relative: one blue can feel warm when surrounded by another that is considerably cooler, turquoise can push an area towards green, and a small amount of violet can take another area in the opposite direction. I do not need to introduce orange, yellow or a conventional red in order to establish these relationships; the chromatic range is much narrower, but those relationships are still there.

Throughout this first stage I worked constantly with these small contrasts, looking for differences in value, luminosity, paint density and temperature. Restricting the palette means that relatively subtle variations begin to carry much more weight. Once this first session was complete, I allowed the painting to dry fully. Something that had initially been a difficulty during the alla prima stage would now begin to work in my favour.

Development of the alla prima stage. Turquoise and violet begin to introduce subtle temperature variations into a painting that still reads predominantly as blue.

Taking advantage of transparency

The relative transparency of these colours can make things more difficult when I want to build an opaque surface, but in a glaze the opposite is true. For the next session I prepared the same colours with glazing medium and, rather than rubbing a uniform film of paint across the entire surface, I preferred to begin by placing the colour down in individual touches. I place the brushstroke and leave it there.

In this way I gradually build small transparent planes over the dry paint and then decide which of them should remain almost untouched and which need to be opened out or softened. In some areas I modify their edges until the transition becomes much gentler; elsewhere I want the brushstroke itself to remain clearly visible.

At this stage I pushed the relationship between the two principal blues considerably further. The light entering from the left-hand side of the canvas, the right-hand side of the model's face, was taken towards 512, our cooler blue, while 515, warmer and more violet, becomes more present on the opposite side. The 539 appears again selectively around the nose and eyes; very little is needed, because even a small amount is enough to alter the temperature of an area in relation to the blues surrounding it.

More general glazes also appear over the arms, shoulders and torso. Some areas had lost depth during the first session, and a thin film of colour allows me to recover it without rebuilding those passages completely. Here, the transparency that had been awkward during the first stage becomes an advantage: I can gradually accumulate colour without concealing everything that already exists underneath.

First glazing stage over the completely dry painting. Colour is initially applied in placed brushstrokes; some remain almost untouched while others are subsequently opened out to modify depth and temperature.

A second glaze and the final adjustments

After allowing the painting to dry again, I carried out a second glazing stage. Some glazes were relatively broad, while others remained much more contained, almost like transparent brushstrokes that I deliberately chose not to soften. At this point the aim was no longer to construct the portrait but to adjust temperatures, recover depth and modify certain highlights while maintaining the same warm-cool logic established from the beginning.

A final, much smaller phase of repainting followed. Some planes had become too dirty after the glazing stages, certain highlights had lost intensity and a few areas of reflected light needed to reappear. In these passages I returned to more direct, opaque paint, recovering only what had been lost.

The main difficulty throughout the process was not really creating distinctions between warm and cool. For a trained eye, those relationships emerge fairly naturally even within such a narrow colour family. The real difficulty was in the darks: once Titanium White is introduced I can work relatively comfortably because the paint gains body and opacity, but in the deepest darks I do not have that option. Each brushstroke allows the layer beneath to participate, and reaching the depth I wanted required an accumulation of paint. The different glazing stages therefore became necessary for another reason as well: they allowed me to build certain darks gradually until they reached the density I was looking for.

The background also received a final repaint. I worked with two very closely related variations: an approximately central area, extending from shoulder height to slightly above the model's gaze, was made a little darker and greener, while the areas above and below were slightly lighter. The difference is subtle because I did not want to divide the background into separate bands, only to introduce enough variation to help support the figure.

Second glazing and retouching stage. Some transparent films extend across larger areas while others remain as clearly defined transparent brushstrokes.

Is it still a monochrome?

Working with such a limited palette forces me to pay much closer attention to value. The reference image may contain a huge amount of chromatic information, but here all of that information has to pass through the few colours available to me, which means it has to be translated. That restriction certainly presents a difficulty, although at no point during the process did I feel that I needed to leave the palette in order to resolve the painting. The differences between 512 and 515 were enough to establish much of the warm-cool structure, 586 allowed me to push certain areas towards green, and 539 provided the warm violet extreme I needed in very specific passages.

After finishing the painting, I still see it as a monochrome. There are violets, small green shifts coming from the turquoise, and clear differences between warmer and cooler blues, but none of those variations disrupt the overall reading of the painting. A monochrome does not necessarily have to mean painting with a single tube of colour; it can also be constructed within a colour family, allowing subtle differences in temperature, value and transparency to expand the colour without the painting ceasing to read as a unified whole.

Detail of the finished painting. The temperature differences are visible at close range: cool and warm blues, subtle shifts towards turquoise and small violet accents.

Try it with your own colour family

Pick one colour family from your own palette. Test every colour in mass tone, diluted and tinted with white before you start. Then choose four and see how far you can take a painting without leaving them.

Explore the Rembrandt Oil Colour range and find your own family of colours.

Painting a Monochrome with a Family of Cobalt Colours

Before painting: really looking at the colours

What Titanium White reveals

Building a restricted palette

A little history

Method: starting with the darks

Moving into the middle values

Temperature within blue

Taking advantage of transparency

A second glaze and the final adjustments

Is it still a monochrome?

Try it with your own colour family

Creating the Monochrome Painting

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Painting a Monochrome with a Family of Cobalt Colours

Before painting: really looking at the colours

What Titanium White reveals

Building a restricted palette

A little history

Method: starting with the darks

Moving into the middle values

Temperature within blue

Taking advantage of transparency

A second glaze and the final adjustments

Is it still a monochrome?

Try it with your own colour family

Creating the Monochrome Painting

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