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March 23, 2006

Photogram - Shadowgram - Image Profiles

Early in the history of photography Thomas Wedgwood, Sir Humphry Davy and Fox Talbot made images known as profiles and published them. The technique used was to places objects that are transparent or translucent, directly onto unexposed photographic paper. This is done in a darkroom under safe-light conditions or in total darkness. One then turns on the ceiling light of a brief moment. This act exposes the paper. Some areas of the paper are completely shielded or partially shielded from the exposing light by the object. Other areas are exposed partially or completely. The result is a latent image of the object. The latent image is a negative image. The technique is not unlike contact printing. Very artistic photograms can be produced. You can place objects on photo paper and then take them out into the sunlight. Strong light will produce a photogram without the need to develop the paper. In this case the image will usually be maroon and white.

The problem is: No matter how done, the image will fade away unless chemically fixed. In this case the word fix means to render permanent. It is a term commonly used in science. As an example when making slides of organic material to view under the microscope, the material will quickly decay, the slide is destroyed, unless rendered permanent by use of a fixodent. Thus the term fix has become part of the jargon of photography.

Melissa, photo papers are sensitized to light using a chemical compound of silver plus one of three other elements. These are iodine - bromine - chlorine. In all cases the compound resembles table salt but slightly yellowish in color. Unlike table salt the crystals are very very tiny. When exposed to light the crystals begin to break down. Under strong sunlight they breakdown by themselves. In the modern darkroom we use a developer to accelerate the breakdown. The true name of the process is called reduction.

When you finish making the photogram using sunlight the image may appears maroon and white. This is because the liberated silver is opaque (black) and the bromine is reddish. When preformed in the darkroom using a developer the image will be black and white as the bromine is washed out by the developer.

In any case the image consists of a mixture of crystals. Some are unexposed and thus un-reduced while others have been exposed and reduced. Unless you intercede, the unexposed unreduced crystals will in time reduce by them selves. Should this happen the whole paper will turn dark and the image will be said to fade.

Fixer to the rescue. The fixer is a chemical that is a solvent for un-reduced silver crystals but not a solvent for silver. One the paper has be bathed in a fixer solution, the un-reduced crystals are dissolved into the fixer. Now the paper must be washed to remove residual chemicals. When done properly the image on the paper will last many many years.

Alan Marcus 50 + years in photofinishing

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March 25, 2006