(From the latin – solar, of the sun and graphia, writing.)

A solargraph is a long-exposure photograph which shows the path taken by the sun across the sky. Solargraphy uses a simple pinhole camera containing photosensitive paper, securely fixed in a position which will not move or otherwise be disturbed. The long term pinhole exposure is made tracking the sun over a period of months, separate light trails form as the sun’s elevation changes relative to the respective hemisphere of the earth, as it travels from its furthest in winter (perihelion) to its nearest in summer (aphelion) .

Solargraphy is a “printing out’ process. This means that the light has to provide all the energy required for the silver halides (salts) on the photographic paper to change to a visible state. When the grains of silver halides on the black and white photographic paper are exposed to light, a few atoms of free metallic silver are liberated. These silver atoms form the latent image. Usually this latent image is then developed using solutions that  reduce (making an atom available to enable the salt to split into its original parts) silver halides in the presence of free silver atoms. An ‘amplification’ of the latent image occurs as the silver halides near the free silver atoms are reduced to metallic silver.(1) In solargraphy no development is done using additional chemicals to amplify the process, so all of the image must be present as light converted silver atoms on the paper.

As more light is allowed to fall on the paper, over the prolonged exposure period, coloured areas form. This is caused by silver atoms clumping on the silver halide particles. As more free silver is liberated by the light energy reaction the ‘print out’ on the paper becomes coloured. First appearing yellow, then sepia, then red-brown and finally as a slate-gray shade as the silver clump particle size increases.(2)

This image may then be scanned to form a digital record. Silver halides remain on the paper where full conversion to exposed silver has not taken place. In a traditional darkroom paper process these would be removed using a fix chemical solution but this may not be possible with the delicate solargraphs due to the bleaching action of most readily available fixes. This means that further exposure to light can completely blacken the solargraph image so they must be stored in complete darkness and only a limited number of scans may be made of the image.

Starting in January 2012, pinhole solargraphs and instructions for use will be produced and distributed amongst the community for placement at various Dunbar locations for 3 to 6 months. The location and participant from the community for each solargraph will be recorded to enable the solargraph to be collected at the end the period. The solargraph paper will be scanned to produce a digital result of the light trails formed.

Characteristics

• Track of the sun across the sky.
• Missing tracks / dot and dash tracks due to clouds over the sun.
• Stationary objects.
• Colours caused by silver halide particles reacting to light and transforming to clumps of silver atoms, the reds and browns of the negative inverting to ‘natural’ greens and blues in the positive (although there is no direct correlation between the actual colour in the scene and the colours formed by the solargraph image).
• Canister movement ghost edges caused by elements, birds, loose fixings.
• Moisture specs and trails.
• Photographic paper degradation from prolonged exposure to the elements.

1. http://en.wikipedia.org/wiki/Gelatin_silver_process
2. http://www.eso.org/sci/publications/messenger/archive/no.141-sep10/messenger-no141-43-45.pdf

Download full instructions – solargraphy.pdf