Just as reflective objects display part of their surroundings, transparent ones show their background. In both cases a photograph always takes in more than just the object itself. An extra complication in the case of transparent objects is that their surfaces are often reflective as well.

The classic treatment for a transparent object is similar in principle to that for a reflective surface – a flood of light, and allowing the structural details to define themselves as shadows and edges. With a transparent object, this means back-lighting, or trans-illumination as it is sometimes known; a broad, even light source forms the background, and the object is placed in front. The more complex the shape of the glass, or whatever the subject is, the better defined it will be, because reflection will cause the edges and thicker parts to record the outline against the bright background.

Practically, trans-illumination can be created within the studio either by using an ear light directed full-face towards the camera, or by reflecting light from a white background. If the object is small enough and suitable to be laid flat, the bright background can be placed underneath, pointing upwards towards a vertically mounted camera. With standing objects, such as a drinking glass or a decanter, one potential problem is the horizontal surface, which can interfere with the trans-illumination; one solution to this is to choose a reflecting surface such as glass or smooth plastic and to use a low, almost horizontal, camera position so that the foreground occupies a very thin area at the bottom of the picture and carries the strongest reflection of the background light.

The structure and edges of a transparent object photographed in this way stand out clearly, mainly because they are reflecting the dark surroundings at the side. This gives the photographer an important control, because the size of the illuminating light source can be varied. The edges of the object will appear darker and thicker if the light covers just the area of the picture and mo more, and if the surroundings are pitch black. This can be achieved by placing the light further back or by using masking tape or black paper to reduce the area, and also by flagging off the sides with black card or cloth. Reducing the area of the trans-illumination has the additional advantage of removing flare problems.

The success of trans-illumination is due to its simplicity of tone – the light appears more as a neutral setting rather than as an identifiable light source. An opposite treatment that can work with some transparent objects is to make the background black. This method, known as darkfield lighting at macro scales, involves directing quite thin beams of light towards the edges of the object to the sides.

The effect is almost exactly the reverse of trans-illumination, for it is the edges and structural details that refract and reflect the light, while the bulk of the object appears black. To confine the illumination to the edges, the light or lights must be efficiently flagged with card or barn doors, and particular care needs to be taken to protect both the background and the lens from light spills. Black velvet absorbs light very efficiently, and is one of the most useful ways of creating a black background.

These two basic techniques are both ways of treating isolated objects. Dealing with transparent subjects in the context of a full set, however, is more difficult, as both trans-illumination and darkfield illumination are rather extreme for regular still life compositions. Usually, the rendering of glass and similar subject suffers, but there are a few partial solutions. One is to place a reflective backing behind the glass, so that its centre does not appear empty. For this to appear acceptable, however, fairly strong refraction is necessary to blend the shape of the backing reflector into that of the glass, and it is a technique that is usually confined to containers filled with liquids, as the photograph opposite shows. In many ways, it is an extreme technique, and there is always a danger that it will appear contrived.

On a pale background, one way of helping to define the shape of the glass is to place dark objects close to its edges. At the sides of the set, black cards or paper can also be positioned so that their reflections are picked up in the glass.