thermography (thûrˌmŏgˈrəfē) [key], contact photocopying process that produces a direct positive image and in which infrared rays are used to expose the copy paper. In a specially designed machine the original is placed in contact with a copy paper containing a heat-sensitive substance. As the infrared rays produced in the machine impinge on the dark or printed regions of the original, the heat generated is transferred to the adjoining areas of the sensitive paper. These areas become dark as well, creating an image of the original. As infrared rays are difficult to focus, the image formed is lacking in sharpness, resolution, and detail. The copies remain sensitive to heat, so that they may darken further with age. The advantages of this process are that it is low in cost and fast and can be performed with simple equipment.
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