AIC's 44th Annual Meeting

The age of digital imaging is rapidly pushing traditional photographic methods into the background. Furthermore, the replacement of discolored analogue photographic prints has become museum display policy, as it is seen as a solution in conservation, and is sometimes promoted by artists. There is therefore an urgent need for methods to characterize photographic materials while they are still available and/or in relatively good condition. Surface properties are some of the most important because they determine the appearance and perception of photographs as works of art These properties are also valuable for identification and authentication purposes. In particular, the roughness of the surface of a photograph determines the glossiness, but also affects the perception of color. Moreover, a surface’s physical character situates the print in time. The photographs materials collection developed by P. Messier, and associated raking light methods for surface texture characterization are a good first step in classifying and identifying photographic materials based on surface roughness. However, in many cases, more direct techniques for measuring surface roughness are required, especially when it comes to assessing the effects of surface treatments. These need to be related to the actual appearance and perception of the materials to allow for better identification, or assessing changes in appearance due to treatments or aging. Over the past 25 years, white-light or laser confocal profilometry has become a standard technique for measuring roughness in many branches of industry. Besides being a non-contact method, the technique measures roughness directly with a resolution down to tens of nanometers, much better than any current optical method. Roughness can be characterized by the calculation of industrial standard roughness values, for example, average roughness, Ra or root-mean-square roughness, Rq. 3D visualization techniques can be used to characterize changes in surface roughness due to treatments or, more generally, the identification of photograph types. Currently, a study is being conducted by the University of Amsterdam and the Cultural Heritage Agency of the Netherlands on the relationship between surface properties and the appearance of photographic materials. The surface roughness of samples from an Agfa-Gevaert photographic sample book (1972 or 1973) was measured using a NanoFocus µSurf confocal white light profilometer, with a spatial resolution of less than 1 micrometer and a height/roughness resolution of 60 nanometers. The results are being related to the perception of a number of conservators and other museum professionals who were asked to judge the appearance of the samples. The results of this research thus far have shown that, when identifying photographic materials or making judgments about their condition, it is important that one considers both the “objective” values of surface properties such as roughness in relation to time and possibilities of the photographic industry, and the “subjective” interpretation of the observer, influenced by interest, cultural background, and time.