Painting en plein air means painting in the open air. It’s a way of working that David Hockney chooses today – but working directly from nature goes back to from at least the second half of the 18th century. During the first half of the 19th century, it was used to spectacular effect by J.M.W. Turner and John Constable. But paintings made en plein air during this period were treated as “studies”, which may or may not have then been used towards larger, final works made in the artist’s studio. It wasn’t until the pioneers of French Impressionism, from 1874, that such works painted alla prima – meaning “first attempt” – from en plein air began to be exhibited as works in their own right.

As an artist, en plein air is a wonderful, direct and invigorating way of working – but there are a few things that can be helpful to think about. Here’s my quick guide to getting started.

1. Choose the right medium for your work

Watercolours, used by J.M.W. Turner, are wonderful for quick, spontaneous en plein air painting. The art of watercolour painting is to think of your white paper as the “light”. The aim is to tint the paper and build up the image using as many transparent layers of colours as necessary. Watercolour is not designed to be used in an opaque way, like a designers’ gouache or acrylic. Use a spare sheet of paper (ideally the same as you’re painting on), and use it to try out your colours on. Have a look at J.M.W. Turner RA’s travelling watercolour box below, with its square trial sheet attached.

For impressionistic alla prima work – remember, that means a final work that’s made in one go, outside – chose oil paint. When dry, oil paint can be built up in layers and create an impasto, à la Monet.

With oil paint, you can use it straight from the tube – but you can also use a “thinner” – a solvent, traditionally turpentine. To build up in layers, add a “medium”. The most common medium in oil painting is the binder linseed oil, and if using this, you’ll also need to combine with your thinner. For the consistency, the golden rule to adding a medium is “lean to fat”. The lean is the turps (solvent) and the fat is the oil (linseed). That means, if your painting is being developed over a period of time, you always start with thinning the paint with solvent and then add linseed oil, starting with less and building up as needed. So, as you proceed, you might try beginning with around 10% oil to 90% solvent, then may add more oil to become more like a 50% ratio, or more.

Experiment with different mediums and materials, noticing the different consistency, texture and finish they give you, and think of the appropriateness of the situation.

2. Plan your colours

Whether you’re a beginner or more experienced, a good basic palette starts with the three primary colours – red, yellow and blue.

However, I’d suggest you’ll need two of each primary colour, one warm and cool. Looking at Moses Harris’s Prismatic Colour Wheel from the RA Collection. Perhaps you take a combination of colours that are the primaries alongside those that sit on either side of each of your three primaries, as laid out below as an example. You can buy pigments in these colours, as listed.

Red

Primary red – such as Cadmium Red (warm)
Purple red – such as Alizarin Crimson (cool, includes some blue)

Yellow

Primary yellow – Cadmium Lemon (cool)
Orange yellow – such as Cadmium Yellow Deep (warm, includes some red)

Blue

Green blue – such as Phthalo Blue (cool, includes some yellow)
Purple blue – such as French Ultramarine (warm, includes some red)

If you have these pigments, you can then mix your secondary colours – orange, green and purple – yourself. Do this by mixing the relevant primaries from above; so for orange, mix your red with your orange yellow. For green, mix your yellow with green blue, and for purple, mix your purple blue with purple red.

Red, yellow and blue mixed altogether makes blacks and browns – and so, as per the French Impressionist Claude Monet, I’d suggest it’s better not to use a separate black pigment. However, essential to add to your basic palette is a white, Titanium being the most common in use today. It is opaque, and the whitest of whites.

To mix greys, add white to your browns, which then can have a biased tint towards any primary or secondary colour. This is one reason for suggesting not to use black, as there are colours within greys.

3. Don’t forget your practical essentials

Portable easel

This is normally of a tripod design. As you’ll be outside where it may be windy or on uneven ground, these may need to be secured into the ground, if possible. If not, I’ve found using a weight suspended from a string attached from the centre helps to make the easel sturdy. I believe it’s such practical challenges – as art is difficult enough! – that led the artist Degas to famously state: “You know what I think of people who work out In the open. If I were the government I would have a special brigade of gendarmes to keep an eye on artist’s who paint landscapes from nature”. Clearly, painting en plein air isn’t for everyone.

It is worth noting that Constable would sometimes work with his paint-box on his lap, with his paper attached to the inside of its lid. Do what works for you.

Palette

Use a wooden palette for oil and acrylic (see Mary Marchioness of Buckingham’s below), or a plastic one for watercolours – although even a plate can work well.

Palette knife

This is for mixing oil and acrylic paint as they help to mix the paint better, as well as saving your brushes from deterioration.

Jam jars with lids

This is for your solvent or water – you’ll need at least two. Keep one clean for thinning the paint, the other becomes dirty for cleaning your brushes. Always recycle your solvent.

Brushes

I’d suggest using hog hair, round and filbert type for oil and acrylic, and pure sable or synthetic, round, short handled for watercolour. Choose a long-handled brush for oil.

Canvas, or canvas board and paper

Or a sketchbook.

Rubber

A putty is best.

4. Choose a motif and composition

Your en plein air “motif”, or subject matter, doesn’t have to be exotic and faraway or picture-postcard – it could be your own nearby environment, possibly a natural or urban landscape. Choose something that you simply enjoy looking at, that you think is beautiful – beauty can be found in the simplest and humblest of places and within the most everyday.

Think of your composition – choose either a sheet of paper or canvas with a shape and proportion that feels good to work with, and start painting straight onto it. Alternatively, draw compositional studies beforehand – always a good starting point. You can use any medium, but you can’t go wrong with simply a pencil and sheet of paper on a board or sketch book – and don’t forget your rubber. Try to keep each study about one main concept – perhaps it’s about the composition, or perhaps it’s just trying to get to know the main subject that you’re depicting. When drawing and thinking about your composition, it’s about discovering the edges, the ratio of the rectangle, height relative to width (or possibly square). It’s common to speak in terms of a “landscape or portrait” format – but remember that great landscapes have been painted within an upright, vertical portrait format, and vice versa.

5. Consider the light and the weather

When painting en plein air your awareness of differing light and changeable weather becomes heightened – you’ll notice the changes not just on different days, but at differing times throughout one same day.

On the back of John Constable’s Cloud Study, Hampstead, Tree at Right, 11 September 1821 he notes: “Hampstead, Sept 11, 1821. 10 to 11 morning under the sun – Clouds silvery grey on warm ground sultry. Light wind to the S.W. fine all day – but rain in the night following.”

In terms of form, painting directly from the landscape is no different than painting a subject within the studio (although, of course, you can experience the added practical difficulties that Degas loathed). So the key question to ask is, what am I painting about?

If it is about the changing light, perhaps have various canvases on the go throughout the day as Monet did. He would then re-visit the relevant canvas on another day when the light was right; his letters of correspondence are full of complaining about the weather. Another strategy could be to work on various quick one-offs in water colour, as Turner would customarily do.

If you choose to work on a painting over a sustained period of time, you may discover that the configuration of the forms and structures within your chosen motif appear very differently from the morning, when the light is from the east, to the early afternoon, where it begins to come from the west. Of course, over various months you will experience where the light may or may not reflect from, as the days either get longer or shorter. Therefore you may choose particular times of day, or weather sunny or grey, and even particular months when to work on your painting. Even within these parameters, the motif at times will visually appear differently to us; it’s also not only natural conditions of weather, light and seasons that changes what we see in terms of colour and form, but the optics of how our brains perceive colour.

The aim is to attempt to remain faithful to your initial idea that you were originally painting about – that’s to say, why you began the picture in the first place. Avoid chasing transitory moments, otherwise you can just end up going round in circles!

6. Look at the whole

We have just spoken about transitory moments, due to weather and light, and the importance in attempting to remain faithful to your concept – this, then, is the essence of working directly from nature and perception.

There is no one way to start a picture. However, a good way is to try to see and paint the motif as a whole, by blocking-in areas as an arrangement of simple shapes and colour sensations. We observe colours interacting with one another; one colour next to its complimentary colour – that’s the colour opposite it on the colour wheel, for example, red and green – will very likely change each other’s visual appearance, from this colour by itself or next to a more similar colour.

For that reason, my advice is never to look at any one part of the motif in isolation, as we will never get a good idea of what colour value that area or form could be. For example, what type of blue is cobalt blue? It looks like a green blue next to the red blue of French ultramarine, but in relationship to a green blue of Phthalo, cobalt looks like a red blue. We must therefore always attempt to see values in contrast to one another and in relationship.

So, these are some of the key things you could think about, for starting to paint en plein air – just as the masters have done over the centuries, and just as David Hockney is doing right now (albeit with an iPad rather than oil paints – as he says, beneficial for easy mixing of colours, and because there’s “no clearing up”).

But, having shared all this advice, I must also say – please just have a go. Enjoy being outside. Experience it and try to capture that, however feels right to you. And let’s just hope you’re a Constable, not a Degas.