'There is a phrase I love: tone does all the work and colour gets all the glory,' says Liz Chaderton. 'Nowhere is this truer than in the world of watercolour. While people will often make comments about a picture’s colours, it is the range of tones – from the sparkling white of untouched paper to the dark of full-strength paint – that captures a sense of volume in the subject you are painting.

'Every strong painting is based on a balance and range of tones so, when tackling a new subject, carrying out a monochrome study is a fabulous way of really concentrating on the subject without worrying about colour mixing.

'In watercolour we alter the tone of our mix by adjusting the pigment to water ratio. We do not have the luxury of adding white to lighten the tone or black to darken it. To add a slight complication, we might have water on our paper or in our brush, which will alter the mix further so being aware and in control of the paint to water proportions is a key skill'.

How do you paint a monochromatic painting?

Two approaches

In the following blue portrait demo (see image below) I aimed for a loose interpretation, but still did a lot of blending; this generally makes a portrait feel calm.

Tonal Blue, watercolour on Bockingford 140lb NOT watercolour paper, (38x28cm)

In the green version (below) I also worked in three layers of light, mid and dark using phthalo green.

Particularly in the mid and dark tones I aimed for the edges of the brushstrokes to be more visible, giving it a more energetic overall feel. It is worth experimenting to see which you prefer and to note how a small adjustment can have a big impact on the overall effect. I also put in a background wash and a little splatter.

It is also important to observe that these two portraits are far from identical or a photographic copy of the inspiration image. If you were worried that tracing or projecting is cheating, see how these two monochrome portraits are such different interpretations.

Tonal Green, watercolour on Bockingford 140lb NOT watercolour paper (38x28cm)

Top tip

People often struggle with the concept that even if the local colour of an object is dark – such as black hair – there will be very light tones within it, as in the highlights on shiny hair. If you find it hard to see tones, use your computer or phone to turn the picture into a black-and- white version and work from that. In the same way, if it is difficult to check on the tonal balance of your painting, take a quick photo with your phone or tablet and again make it black and white. It will really help show up any problem areas.

The old-fashioned technique is to squint!

Try this!

Start by selecting a single colour.

Choose one that is dark in its strongest form. Intrinsically, yellow and some pinks are light colours. Even at full strength they are only mid-tones so choose a colour that is capable of being dark.

On a scrap of watercolour paper (I cut up old paintings and use the back), mark out seven or eight squares.

Add just enough water to your paint to encourage it to flow and paint the first square; this is your darkest tone.

Now add a little water and paint the next. It should be perceptibly lighter, but only by one step.

Continue in this way, aiming to have just a tint of colour by the end of your boxes.

It’s trickier than you think to achieve that nice even graduation. You can see my mid-tones are too close.

Demonstration: Tonal Blue

Your reference photograph

This photo comes from Pixabay. (pixabay.com) and is copyright free.

My pencil lines in the following demonstrations are stronger than I would normally make them so that they show up here. Try to keep them light or even use a blue pencil that will blend into your work.

I used a quarter sheet of Bockingford 140lb NOT watercolour paper for this practice portrait. I suggest you use A4 or a quarter sheet so that you have space to let the water flow, but it won’t take too long to complete.