PRINTING INFRARED NEGATIVES ON TRANSLUCENT PAPER

As a non-destructive method in the examination of paintings infrared photography has an increasing importance in practical restoration and the study of underdrawings: infrared photographs are frequently compared with x-radiographs for such purposes. Infrared photographs generally show a superposition of the visible image and other elements not differentiated by the human eye, but revealed in the wavelength region for which the infrared film has an extended response. Overpaintings can be discriminated in this way and damaged areas localized; changes in composition and underdrawings can be partially revealed. The image of the elements in the infrared photograph \vhich are also visible to the human eye has a density much superior to that of the specific infrared elements: the photographer has thus to work with very high densities in order to obtain a correct contrast in these elelnents made visible by infrared photography. In this respect the infrared negative contains nlore information than the positive print on paper, which is often incomplete. By using certain masking techniques [1] in which the infrared negative is superimposed upon a positive of a panchromatic film exposed with a red filter, this problem has been solved in part: great differences in density of the negative are balanced with a contrary density, and the visible image is thus annulated. Although this technique emphasizes the specific aspects of infrared photography, it demands an exact and complete superposition of the infrared negative and the panchromatic positive, which is very difficult to achieve when enlargements are required. Frequently in infrared photographs the underdrawing is visible in some areas and invisible in others; utilizing the superposition process may then annihilate the visible underdrawing. In view of these difficulties an attempt was made to obtain reasonable prints of infrared negatives permitting an easy enlargement to the scale of the painting by utilizing translucent photographic paper. This paper (Kodak Kodalith TP) nlust be developed in a normal paper developer until the areas with a high density in the negative have a good definition. In viewing the print in reflected light it appears too dark and foggy. In transmitted light, however, the various densities are well differentiated, allowing a complete 'reading' of the infrared negative. The prints on translucent paper can be studied on a negatoscope together with x-radiographs; as they can be easily enlarged to the format of the x-radiographs a precise comparison is made possible.