William Gilpin‘s 1768 Essay on Prints had the aim of outlining ‘the Principles of picturesque Beauty, the Different Kinds of Prints, and the Characters of the most noted Masters’. The work defines ‘picturesque’ as ‘a term expressive of that peculiar kind of beauty, which is agreeable in a picture’. Gilpin travelled widely throughout Britain, noting those aspects of the landscape that tended towards the picturesque.

His Observations on the River Wye and several parts of South Wales (1782) is a description of this part of the country ‘relative chiefly to picturesque beauty’. Gilpin notes that, 

Many of the furnaces on the banks of the river consume charcoal which is manufactured on the spot, and the smoke (which is frequently seen issuing from the sides of the hills, and spreading its thin veil over a part of them) beautifully breaks their lines, and unites them with the sky.