The Victoria and Albert Museum
A Claude Glass is ostensibly a small, blackened mirror which is contained in a box. The device acts as a portable drawing and painting tool which was popular in the late Eighteenth Century with the amateur artists who embarked on international “sketching tours.”
The device was especially meant for us in rendering landscapes by reflecting a landscape so that it could be copied by the artist. The reflections of the landscape, it was said, resembled some of the characteristics of the Italian landscapes by the famous Seventeenth-Century painter and sketcher Claude Lorrain from whom the instrument gets its name.
The instrument consists of a slightly convex blackened mirror. The artist would hold the glass up to his or her eye, allowing the scenery behind the viewer to be seen as opposed to that in front. The convexity of the mirror served to reduce the dimensions of extensive views into those more suited for a small drawing. The mirror was blackened (as opposed to a normal silvered mirror) served to produce a somewhat weaken the reflection, making only the most prominent features stand out. This also reduced the intensity of the colors. The resulting image was thought to be a more picturesque view of the landscape.