Posted on Thu 12 May 2016
The chromatics of a blue sky are applicable to all media – the names of the paints are basically the same, it’s the behaviour of the pigment that is different. I shall concentrate on the hues. A blue sky is redder directly overhead; as it grades towards the horizon it goes through a green phase until it starts to be affected by light reflected from the land.
Sky colours – the basics
For a red blue you could use ultramarine, but that precipitates, giving a grainy effect that does not look real. What is needed is transparency, so try Winsor blue (red shade) or phthalo blue, although that is not as red as ultramarine. You then grade into the Winsor blue (green shade) or you might like to use cerulean blue, which is green biased – but do check as ceruleans do precipitate. Cotman cerulean is transparent and dries much like phthalo blue. These pigment characteristics only apply to watercolour painting.
A graded wash is one of the first techniques in watercolour painting and is worth practising; the key is not to stop and fiddle – see the basic wash (below). You may wish to introduce more colour into the wash; I often add permanent rose, followed by raw sienna, towards the horizon. This gives a roseate hue that implies a little sunshine and relieves the monotony of the blue. If working in oils or acrylics the grading can be done using a hog-hair fan blender. For certain skies try subtle over-glazes of cerulean and ultramarine.
Sometimes it is enough to include a particularly interesting development you have noticed. On the other hand, you can simply make it up! Why not? It is worth studying cloud systems – they are varied and fascinating. With a little knowledge you can look up and identify the various types, building up a mental library of shapes. All forms of cloud formation require special techniques to depict them, especially in watercolour. But once mastered, your sky paintings will never be boring again.
There are three basic ways I produce cloudscapes. The first is to leave cloud shapes out on the dry paper – diminishing shapes generate perspective in the sky. Once the paint is dry you tint in the shadow sides of the clouds – remember to note the position of the sun! This tinting needs to be a transparent grey, ideally non-precipitating; I use a delicate mix of phthalo blue and lemon yellow. If, however, you want to depict a malevolent stormy sky with lashing rain use indigo and raw umber, which will precipitate very well and you will get all the drama you need.
The second method, working on wetted paper, will give you soft clouds. Again, negative-paint the clouds, but if the paper is very wet they will bleed a lot. As the paper dries the clouds will merge less – judging the effect you need is born from experience. When the paper is dry, re-wet it and tint the clouds.
The third technique involves spraying the paper lightly with an atomiser, then painting the negative shapes again directly with a hake – this gives a hit-and- miss effect.
These methods can also be used one after the other, but allow to dry between each or you will end in a mess. Additional drama can be added by introducing splattering, sponging (for light shafts etc), picking (for stars), sanding for graded effects, and lifting with soft tissues – this is especially good for cirrocumulus.
Next time you are outside, look up and check out the sky, and then work out how to paint it using these tips.