“The most important of [the] tourist knick-knacks [of Georgian England] was the so-called Claude glass. Sometimes a piece of coloured glass through which to look at the landscape, it was more usually a convex mirror that miniaturized the view and, in its compression of the landscape, made it look more general and uniform. It was a tool for capturing and manipulating nature, for making a frameable possession, and it required you to turn your back on what you wanted to see. In 1769 the poet Thomas Gray described looking at Derwentwater in the Lake District . . . using his Claude glass: ‘saw in my glass a picture, that if I could transmit it to you, & fix it in all the softness of its living colours, would fairly sell for a thousand pounds. this is the sweetest scene I can yet discover in point of pastoral beauty.’”

—John Brewer, The Pleasures of the Imagination: English Culture in the Eighteenth Century, 1997.