Joseph Mallord William TurnerSeascape with Storm Coming On c.1840

Unfinished works, such as this, provide an opportunity to scrutinise Turner's techniques closely. Though the process has been interrupted, these pictures reveal much about how he built up his images.

Turner has begun this work with two distinct areas of colour for sea and sky, washed in very broadly. He used a similar method in the large batch of watercolours known as 'colour beginnings' that he produced from the late 1810s onwards. The lower of the two areas is an extraordinary golden colour, permeated by passages of grey and black. The surface is further animated with light, but very deliberate, touches of white, green and brown.