Cox's late watercolours on coarse Scotch wrapping paper anticipate Impressionism by three decades. The rough surface forced a freedom that smoother papers would not have allowed: broad washes, ragged edges, atmospheric effects that dissolve solid form into light and moisture.

He was born in Birmingham in 1783 and was largely self-taught. He became one of the great masters of the English watercolour tradition, painting Welsh and English landscapes with a directness that his contemporaries found crude. He taught drawing for much of his life and published influential treatises on watercolour technique. He died in 1859.