I used a size 12 sable brush and Whatman 200lb (410gsm) Rough paper on a board. Tilt the top of the board up by one or two inches (2.5 to 5cm) during the wetting process so that water spreads. Excess fluid at the bottom is mopped up with a brush or soft tissue paper. Thereafter lay the board flat for more predictable diffusion of the paint. I usually wet the paper with full brushloads of clean water using a size 12 for a 12x18in. (30.5x45.5cm) painting and a size 10 for a 10x14in. (25.5x35.5cm) painting. Cover a small section at a time so as to spread the water evenly. Long sweeping strokes may leave dry streaks on the surface. A larger brush such as a squirrel hair mop will speed up the process. Too much water may cause slight surface undulation, leading to puddling or uneven drying, but not if you tilt the board. Sometimes I deliberately leave small areas or streaks of dry paper for highlights, as in this demonstration. Owing to the roughness of the surface and the sizing of the paper, these dry brush effects are irregular and their random appearance imparts a liveliness to the cloud composition.
Starting at the top edge with French ultramarine, I laid down a triangle of blue sky with irregular scalloped edges, being mindful that I was creating negative spaces of white clouds. A horizontal wash of the same blue gave form to the long diagonal white cloud on the right. When creating white cloud spaces, remember to make allowance for diffusion of pigment. A 2in. (5cm) gap may end up with only half the amount of white space. Do not worry about jagged or irregular edges as they will soften as diffusion progresses.
A small amount of strong French ultramarine was dropped gently on the borders of the cloud with dry white edges in the centre of the sky. This enhanced the tonal contrast, thereby establishing a visual highlight.
A grey mixture of French ultramarine and burnt umber provided a shadow for the large white cloud on the left. The lower edge was then darkened with a stiffer mix of the same colour. Above it, a lighter, bluer mix gave form and a subtler shadow to the upper half of the cloud.
A narrow horizontal wash of cerulean blue was laid beneath the lowest clouds and, below that, a wash of raw sienna. In the UK the blue sky ranges from ultramarine blue high up, to cobalt in the middle and cerulean lower down. Often it is pale yellow near the horizon. This can be explained by the diffraction of light through moisture in the atmosphere, which becomes progressively denser towards the horizon.
Finally, a thin grey cloud was drawn across the lowest part of the sky. Visual recession is created by depicting progressively narrower clouds towards the horizon.
Feature taken from the August 2008 issue of The Artist.