Painting with Light

Stained glass is the only art form that relies entirely on natural daylight for its effect. Every other art from painting and sculpture to tapestry and jewellery is designed to be appreciated by reflected light. In creating such works of art, no great problem arises for the artist. He controls his colours or his shapes knowing that the purely physical reflection in the spectator’s eye will be exactly as he plans it.

With a stained glass window, however, the artist must control a powerful energy which will be transmitted through his medium of expression. He has to paint with light itself. While the painter or sculptor can arrange for the best possible lighting of his work and knows that in essence it will remain more or less unaltered, this is not so with stained glass.

When a window is fixed in its permanent frame in a building, it becomes subject to radical alterations of intensity from influences outside the artist’s control. The medieval glazier, in this respect, had a great advantage over his twentieth century counterpart. He had a setting for his windows that had grown with his own tradition. The architect therefore understood his problems and did not present him with an environment that militated against his work, as so often happens with modern buildings.

The colour of the glass may be bleached and the effectiveness of its paintwork diminished by strong sunlight. Sometimes the sun may shine only on part of the window’s surface with disruptive consequences. The light may advance some colours and make other recede. It may cause two juxtaposed colours, such as red and blue, to combine in an unintentional hue.

Serious disruption may occur, too, from trees or buildings in the vicinity. They may make the lower half of the window dark and the upper half light in contrast. Blue skies or dark clouds may alter the whole colour pitch of a window. A stained glass window is also subject to halation, the phenomenon of light flooding around a solid object and producing a blurred effect. As a result of halation, a black line appears to have its edges eroded and thus seems thinner than its actual width, or a patch of white surrounded by solid black can appear larger than it is. In York Minster, for example, there are restored portions of fourteenth century windows surrounded by clear glass, and here can be seen the baleful effect of competing light values which the restorer, concerned with archaeological exactitude rather than aesthetics, failed to appreciate.

By far the most serious effect of halation is glare – a bright mass of uninhibited light either within a window or coming from a nearby source. This unfortunate condition of glare, resulting from light windows in proximity to richly coloured windows, can be seen in many churches and cathedrals. The only way an architect can have stained glass and still achieve a light interior, is to fill the windows with grisaille – clear glass enriched by painted patterns. Much of the sublime impact of the windows in Chartres Cathedral, for example, is due to the fact that the extensive stained glass is all within the same tonal range and is undisturbed by any white light source.

The glazed ‘canvas’ is subject to a mass of conflicting stimuli from the differing behaviour of wavelengths of colours and their intensities as they reach the eye. The complicated problem of what happens to various colours when they are seen by transmitted light has preoccupied many theorists. The most widely quoted is Eugene Viollet-le-Duc, the nineteen century French art historian. Viollet-le-Duc was mainly concerned with the phenomenon of irradiation, the optical effects of transmitted light through translucent colours, and the fact that this irradiation is unequal according to the colour – some colours recede and others advance, or spread. The most common example of this is demonstrated by the alleged tendency of red to recede and that of blues to advance, often gathering a power out of proportion to the area they occupy. Yellow appear to remain neutral, advancing only if its colour is moved along the spectrum from the red to the blue end.

The broad observations of Viollet-le-Duc are, of course, correct in so far as colours present different optical values, but he and other theorists, tended to explain their differences in dogmatic scientific terms. As James Rosser Johnson, a distinguished American art historian points out, the deeper the shade of blue, the colour most often used as an example in this connection, the less the colour expands. Even reds, which are said to have low brilliance and high saturation, have differing optical values. If for example, a piece of copper ruby antique glass is placed next to a piece of glass coloured red by the non-metallic element selenium, the brilliance of the selenium-coloured glass compared to the antique glass is striking. This kind of brilliance is the opposite of the depth and tonality of colour which the artist requires to eliminate coloured glass as well as white light glare.

In a stained glass window, the artist creates an area of coloured light, modified by monochromatic paint, which offers itself as a kind of music of light, instantaneous in space, energized by the physical properties of light waves in the same way the music is energized by the behavior of sound waves. Like the composer, the glazier knows how the light will behave as it passes through various colours, controlling the irradiation of some colours so that they do not overpower the essential theme and harmony of his composition. This knowledge is the subtle combination of workshop rules, inherited from a long and living tradition, and his own intuitive co-ordination of balancing coloured images.

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The Medium of Stained Glass – A distinctly dynamic art

Stained glass is unique among the arts of the world because of the relationship that exists between glass and light. We see colour on a painted surface through the reflection of light. The colour we see in a stained-glass window is from the light refracted or transmitted through it. The colours of the glass are deadened by reflected light, and when darkness falls, a stained-glass window becomes dark and cannot be brought to life unless some form of artificial illumination is transmitted though it.

Essentially a dynamic, daylight art, stained glass is energized through its relationship with light and changes according to the time of day, the seasons and the weather. All affect – sometimes subtly, sometimes dramatically – the image that is perceived, for stained glass is the oldest and cunning form of kinetic art.

The Medium of Glass
Glass is an amazing substance which sparkles with diamantine brilliance and can also be as deeply infused with colour as a gem stone. Although man-made glass has a long history – more than four thousand years – even today scientists do not know the precise nature of this enigmatic substance. All they can say is that it is formed by melting certain minerals and cooling them in a way which prevents crystallization, giving a super-cooled liquid that is stiff, or of such high viscosity, that it has most of the properties of a solid.

Transparency
Glass which has been made by melting a pure mix of silica, soda and limestone at about 2700 degreed Fahrenheit, produces transparent and colour-less glass. Unlike such solids as wood and painted canvas which reflect light, the molecular structure of glass allows the energy of light to pass through directly so that in a perfect sheet of glass the light rays enter and emerge at the same angle with their original brilliance unaltered and without distortion. Variations in thickness and small flaws in the glass, or on its surface can however deflect the rays of light. These changes, which concentrate or diffuse the light, create a fascinating and ever changing shimmer and iridescence. For this reason stained glass is manufactured by a process which encourages imperfections.

Colour
There are two basic methods of colouring glass. In the first method, certain metallic oxides can be dissolved in glass, and the molecular structure of the solution is such that it absorbs some wavelengths of light and transmits others. These unabsorbed or transmitted wavelengths of light give the glass its colour. Glass to which iron oxide has been added, for example, is green. In the other basic method, chemical particles may be dispersed or suspended in the liquid. If they are approximately the same size as the wavelength of light, certain colours will pass through the glass while other are stopped. Particles of gold, for example are dispersed through the glass to give the characteristic ruby red colour.

It is almost miraculous that very early in the history of civilization, man, as a result of his ingenuity, almost fully developed glass – this amazing substance which sparkles with diamantine brilliance, which has as fascinating an iridescence as an opal and which can be as deeply infused with colour as a ruby or emerald, or sapphire. Quite apart from the story or image a stained glass window may convey, it is the jewel-like qualities of glass which make it a unique work of art.