This book contains the results of studies carried out during 1986 and 1987 by the CRCDG. A new concern of the center is the conservation of archaeological leather. A study has been dedicated to the treatment of waterlogged leather attifacts, in order to ensure their preservation when they are excavated. Another study deals with the effects of air pollution on paper which has been deacidified using two different methods. The study will be further extended to alcoholic deacidification methods. The first results raise some important questions. Transparent papers are extremely difficult to preserve, due to their fragility and sensitivity to atmospheric variations. Thanks to a better knowledge of these papers, obtained by the study of the various fabrication processes and the analysis of fragments of old tracing paper, a repair method which is quite satisfactory has been worked out. Silver-gelatin negatives on glass plates are often broken or cracked. To repair them, several adhesives have been selected according to criteria of solidity and compatibility with the silver image. Also in the field of photography, the researchers have studied the yellowing of certain negatives which have been reinforced with mercuric iodide. A better comprehension of the yellowing process has led to the definition of a chemical method to restore the original color of the photograph. The analysis of several vegetal tans used for the fabrication of binding leather has been carried out by various chromatographic techniques. The results have been applied to the study of free tans extracted from leather. The last article gives the results of colorimetric and spectrometric analyses of two drawings by Constantin Guys kept in the Musée des Arts décoratifs in Paris. -- AATA