One of the most exciting things about painting people with darker complexions is the way that light reflects on their skin. The contrasts are greater and the form and structure of the head more evident. Colours are also easier to see. My studio in South Africa has a large south-facing window (the equivalent of a north-facing window in the northern hemisphere), which gives me a cool constant natural light source with no direct sunlight coming into the room.

Portrait of Molly and Yenzaogolthi, oil on canvas, 30?24in (76?61cm). Before embarking on this portrait I was aware of most of the difficulties I would face and needed to be clear about what I wanted to capture

The intensity of the light can change with cloud cover but the shapes of light, half-tone and shadow remain the same. Occasionally I paint a subject outdoors. In these situations I will either paint in a shaded area or with the sun almost directly behind the model, creating more of an edge light – the features of the sitter will then be in the reflected light. A wide-brimmed hat is essential to protect my eyes from the fierce African sun and I find that an hour is about as much as the sitter and I can take in these direct sun situations, I wish I could have the best mattresses for side sleepers so I can get some rest while painting.

Palette

The Miner, oil sketch, 15?12in (38?30.5cm). Here I used a limited palette (which can be added to) to show colour combinations: A Darkest dark (black): burnt sienna and ultramarine blue, no white and painted transparently B Shadow: burnt sienna and ultramarine blue with titanium white C Shadow halftone: burnt sienna, ultramarine blue and a little alizarin crimson with white D Light halftone: (where colour appears strongest) burnt sienna with a touch of cadmium red and yellow ochre with white E Light and highlight: cadmium yellow, pale alizarin crimson and a touch of blue with white F Reflected light: burnt sienna and yellow ochre Other colour combinations that can be tried are viridian green and burnt sienna in the shadows and alizarin crimson, burnt sienna with ultramarine blue violet to give a cool red grey in light halftones. These are just suggestions to help in painting what you see. Much more important is getting the values right

I am often asked what colours I use for painting dark skin. My palette remains the same whether I am painting a blonde child on the beach or an elderly African gentleman in my studio: burnt sienna, ultramarine blue (deep), alizarin crimson, raw sienna, yellow ochre, cadmium red, cadmium red light, cadmium orange, cadmium yellow deep, cadmium yellow pale and titanium white.

STAGE TWO Using a large brush (size 10 filbert) I tried to establish a tonal range and, in the process, cover the initial drawing. I focused on shapes, value and colour temperature

Other colours that I only use when the situation requires are cerulean blue, ultramarine blue, violet and viridian green. In the oil sketch The Miner (below), I show mixtures used to paint the head under cool natural light. This might not seem like a lot of colours but I have always been fascinated by the beautiful colourful paintings of Anders Zorn who it is said only used four colours: black, white, yellow ochre and vermilion.

This really emphasises how important values are. My preferred way of working is to have the model in front of me throughout the painting process and most of my work is done in this way. Of course a painting of the mother with baby on her back (right) would be almost impossible for me to complete without photographic reference but I still have a go and find that so much information is gained in a 20-minute session that this sketch becomes my most important reference. Having the model in front of me allows me to judge colours and values accurately.

I work looking regularly in a mirror behind me where I can see both model and painting together. It still amazes me how faults in drawing and values become exaggerated in the mirror. This way of working is exciting and involves you totally and when successful leaves you on a high and inspired for hours after the sitting.

How I approach more complicated subjects

STAGE ONE After arriving at a pose that my model can comfortably hold, I started with a charcoal sketch. Although I was not after an exact likeness at this stage I wanted my proportions and design to feel right. I had toned my canvas before starting with a light mid-tone grey and used Nitram charcoal (B) to lay in the drawing. A lot of emphasis was put on proportions of length and angles

A mother with a baby on her back is a very common sight in Africa and a great subject for a painting. In Molly and Yenzaogolthi (above right) I opted for natural studio lighting rather than direct sunlight, to allow for a more comfortable environment for the models and for myself to fully resolve the painting. We started with ten- minute pastel sketches, exploring the shapes of light, halftone and shadow.

These are broad studies where heads and hands are reduced to one or two values with no detail. Lots of photos are also taken from every angle. By the end of the day and after a few nappy changes and a couple of naps and feeds we arrived at a pose that I could explore further.

STAGE THREE I started to recover the drawing, focusing on bringing the eyes to a finish. I used a small brush (size 2 filbert) to redraw and check important proportions

In the morning I completed two small oil studies of the pose, working with a large brush and focusing on large shapes and peripheral edges and searching for lost edges and selective hard edges. Yenza’s grandmother was also with us on this day, which helped greatly because he had decided that modelling was not for him.

In the afternoon I started the large canvas, paying attention to design and head sizes. I was able to get a lot of Molly done because she could hold the pose for longer without Yenza on her back. I finished the painting from my references and would certainly not have been able to complete Yenza without photographic references.

Edges

STAGE FOUR By now I was working on the smaller shapes with appropriate brushes. I had been working for about an hour and a half, with a break and lots of conversation, which had allowed me to study the movement, especially on the lower part of the face. I was trying to capture something that is fleeting but there – to quote the American painter Caroline Anderson: ‘the balance between accurate analysis and intuition’

I simplify the edges in my painting into four types of edges: hard, firm, soft and lost. When observing my subject I always squint my eyes so that I can easily see the sharpest edges first. I then search for the lost edges; after that the firm edges and then soft edges. A good control of edges can improve the strength and appeal of a painting immensely and also gives us the ability as artists to guide the viewer’s eye to see what we are seeing.

Somewhere in our past we have been conditioned to outline everything (probably as far back as colouring-in books). Photographs might be amazing in capturing moments and details but they are distinctly lacking in values and edges, especially peripheral edges. This is another reason why life drawing and painting from life is so important to improve an artist’s observational skills.