View this artwork by appointment, at Tate Britain's Prints and Drawings Rooms
Technique and condition
This sketch is on white wove paper with a Whatman watermark and date of 1816. The composition has been built up with localised washes of a single pure colour applied to dry paper, with any initial pencil drawing. Turner may have avoided his common technique of soaking the paper first, which would enable a very even or graded wash to be created, because the sheet formed part of a sketchbook when he was using it.
The range of colours is limited: Prussian blue, or vermilion for the pink washes, in combination make up the distant mountains. Yellow ochre was used for the pale yellow foreground, and applied over the pink and blue washes at a later stage of development, to create the nearer mountains. Pure Prussian blue was used for the water. More intense shades, as in the water, were achieved by building up several successive washes of the same colour.
Examination at moderate magnification, up to x40, made it clear that the blue, pink and yellow colours were each painted using a single pigment. The identifications of these materials were in fact confirmed by removed tiny samples the size of a pin-point, and placing them in the sample chamber of a scanning electron microscope, under an X-ray beam. This beam interacts with the elements that make up each pigment, and the resulting spectrum makes it possible to work out which elements are present. Since it is already known that the washes are pure colours, it is then possible to work out exactly which pigment was used in each case. Visual identifications of these materials can then be made on other watercolours, when it is already known from examination at moderate magnification that the wash consists of a pure pigment and not a mixture. In a complex and finished watercolour with multiple overlying washes, it would be foolish to attempt such visual identification.