Photograms continued
A strip of the same photographic paper you are going to use for your photogram is placed under the enlarger or other light source. Cover one end of it with a card and switch the light on, move the card covering a series of timed steps then process it. What you are aiming for is a test strip (tonal pallete) showing distinct tonal patches from the base white of the one not exposed to light to the maximum black of the one exposed for the longest time Arrange a number of leaves on the paper and using this 'tonal pallete' as a guide switch the light on and remove them at similar time intervals process paper as for test strip You should see a variation in tone the last to be removed giving the lightest tone the first the darkest. |
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One of the earliest recorded exponents of this technique was Thomas Wedgwood who in 1800 was experimenting with silver salts. He found if he placed objects on paper which he had coated with a solution of these salts and left them out in the sun for a considerable time, an image was formed by the darkening of those areas exposed to the light Unfortunately he did not find a way of making the image permanent and dropped the idea. |
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In 1834 Henry Fox Talbot the father of Photography (as we knew it until digital came on the scene) in particular the negative image process, found a way of fixing the images he produced and called them 'Photogenic' drawings . He used the technique to assess the light sensitivity of the emulsions he was producing by placing various objects such as feathers lace etc on them and then exposing to various levels of illumination a process very similar to the Sun Printing exercise in Unit 1 He went on to increase the sensitivity of the system in his 'calotype' process where he chemically magnified the effect of a very low level of exposure at an atomic level (latent image) which was not visible, into a visible one by the action of what we know as Developer i.e. the Developing out Process. |
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It is not just conventional photographic emulsions based on silver that posses the property of photosensitivity as an sun worshipper or Botanist will confirm. Millions of people every year are walking photograms where skin exposed to sunlight has turned brown due to the action of ultraviolet rays on the pigment of the skin.
This photosensitivity is contained in the chloroplast's. cover a leaf with a cut out mask and leave in the sun for a day then test the leaf for starch which show up in the shape of the cut out - 'photoleafagram' .
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