On Reflectionby Jonathan Miller, Valerie D. Mendes, National Gallery of Great Britain Staff
In this beautiful book, Jonathan Miller describes our perceptual capacity to recognize real-life mirrors as well as those in pictures, a complex psychological process of which we are usually unaware. He does so by investigating the pictorial representation of sheen, shine, glimmer, and gleam through a wonderfully varied selection of paintings and photographs drawn from the National Gallery, London, and other international collections. With excitement and innovation, Miller provides a guide to reflecting on reflections, enhancing the reader's enjoyment both of everyday life and of visual art.
- National Gallery Publications, Limited
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Light and lustre
Between the two extremes of matt and mirror there is a continuous series of intermediate forms, to which various familiar terms are applied -- gleam, shine, flare, glimmer and of course lustre -- and the appearance of any one surface depends on the extent to which it scatters the incident light, as opposed to reflecting it in a strictly rectilinear fashion. In surfaces with a relatively coarse microscopic texture, the proportion of scattered reflection is comparatively large, so that the light which is reflected in a more regular order is barely detectable as an indistinct gleam or highlight whose colour is similar to that of the source. If the surface is illuminated by relatively colourless daylight, the flare will effectively bleach the local colour of the surface. If the illumination is strongly tinted, the highlight will be dyed with the same colour. In contrast to scattered light, which rebounds in many different directions and is therefore visible from any viewpoint, the rays which are reflected in a more orderly fashion rebound in one direction only, and unless the observer happens to view the surface along the principal axis of this reflection, the highlight disappears. Leonardo da Vinci was one of the first artists to recognise the way in which the visibility of lustre varies according to the observer's viewpoint. He distinguished two forms of reflected light: so-called lume by which he meant randomly scattered light, and lustro which was responsible for the gleam which is to be seen `on the polished surface of opaque bodies'. According to Leonardo the lustre `will appear in as many different places on the surface as different positions are taken by the eye'.
The optical instability of lustre varies according to other factors, one of which is the size of the luminous source. When a surface is illuminated from a relatively small source -- say a distant window -- the visibility of the reflected highlight is critically dependent on the viewpoint, whereas if the scene is more broadly illuminated -- say from the sky -- the reflected lustre is relatively widespread and the visibility is comparatively resistant to changes of viewpoint. Even so, the fact that a highlight is preferentially reflected at one angle rather than another means that the lustre unmistakably fluctuates when viewed from different positions. This is not observable, however, in pictorial representations, since the highlight is depicted on a two-dimensional surface and cannot vary as spectators change their position. The same applies to the legendary eyeline of a portrait which is said to follow the spectator around the room. It does no such thing, of course. The gaze, like the lustre, is represented on a flat surface and it cannot change its appearance with alterations in the observer's position.
Another factor which influences the visibility of lustre or sheen is the curvature of the surface from which it is reflected. Highlights which are thrown off from sharply angled surfaces come and go with captivating abruptness, should either the object or the observer shift. This is why diamonds glitter or scintillate when twiddled in the incident light.
Another characteristic of lustre is the fact that it seems to hover somewhere below the surface in which it appears. In contrast to the local texture anti colour of the object, which are coextensive with the plane of its surface, the sheen or gleam appears to be in the depths. Once again, this is less apparent in a flat picture than it is in three-dimensional reality.
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