The gloomy Claude glass is a convex blackened mirror designed in the 18th century to aid artists and tourists to create landscape paintings. They would turn their back away from the landscape and instead view it in the mirror, which would present a vast scene in a more manageable size whilst also subtly harmonising the tonal values of the view.
Claude Lorrain (1600-82) was a leading 17th-century landscape painter who worked in Rome and became famous for drawings and paintings displaying a subtle gradation of tones. His work became immensely popular in England in the 18th century. The Reverend William Gilpin, an amateur artist, advocated the use of a Claude glass saying, 'they give the object of nature a soft, mellow tinge like the colouring of that Master'.