Technique and condition
This sketch on white wove paper has dramatically altered in appearance, owing to over-exposure to light while it was covered with a window mount that was placed skew. This may have been done to make the hastily-sketched horizon appear level. From Turner’s viewpoint, a level horizon would not have been vital for a rapid colour study such as this.
Originally, the sketch illustrated the contrast between a purplish grey cloudy sky, and a brownish green foreground landscape. Turner often used ‘optical’ or mixed greys and greens. All his contemporaries did the same for greens, for the good reason that there were no useful, strongly coloured green pigments to use directly, until the early to mid-nineteenth century. Artists mostly used indigo for the blue component, and any of the earth colours to mix in: brown ochre, raw or burnt sienna, raw or burnt umber. All these earth colours are familiar today, and still feature in watercolour boxes. For grass greens they mixed indigo with yellow ochre, or a yellow lake, Indian yellow or gamboge. The last three faded even more readily than indigo does, which is why many landscape areas in watercolour tend to look bluish, having lost some of the yellow. Indigo was commonly used for the sky as well, mixed with Indian red or in Turner's case the brighter red vermilion, and darkened with black. For really intense landscapes or skies, Turner substituted Prussian blue for the indigo. Such mixing gave many more gradations of colour than simply thinning down a black wash to give a neutral grey. And most artists who had mastered such methods continued to use them all their lives, even when green pigments became available.
The colour alteration here is extreme. It is a combination of blue lost from the indigo and vermilion red mixture used for the grey sky, the same blue lost from the indigo and brown ochre mixtures used for the foreground landscape, and the white paper having yellowed severely where it was exposed to light. It is still possible to see some of the intended effects in the sky: greyer and darker clouds to the left side, which had black mixed in as well. On the right, there was less red used generally, and more local variation, so the clouds were more bluish purple on this side, and paler towards the horizon. The vermilion has survived well. There seems to have been less shading in the landscape, to judge by what has survived round the edges. If both components of the mixture have faded it is naturally impossible to work out what may have been the intended appearance: here it takes some effort, but it is possible.