General indications are first given about the purpose and the use of surface modification techniques in art. The activity in this field at the "Centre de Recherche et de Restauration des Musées de France" is then described: surface assessment, techniques of restoration, recommendations for conservation. The authorized range of scientific investigation on patrimonial objects is discussed. A methodological analysis of various surface characterization methods and surface treatments is proposed. A limited number of demonstrative examples show the application of these methods in different areas at the Louvre.

Ancient artisans conferred special colourings to their metal artefacts by particular techniques, which went lost in later centuries. They were also able to give to copper based alloys the appearance of precious metals. The author presents ancient examples of coloured metals and alloys, identified by scientific methods and discusses the problem of recognizing various surface treatments on archaeological objects.

A goniospectrophotometer is used to analyze the back-scattered light, in the visible range, by a 0.3 cm2 surface. The measurement is non-destructive, without contact and can be implemented in situ. For a metallic surface, the reflected intensity is measured as a function of the back-scattered angle. The probability density of the normal to the surface is then deduced. The ratio roughness r.m.s. / correlation length is calculated. The method is applied to characterize the different techniques for gold backgrounds in primitive European paintings. For a non-metallic surface, the reflected intensity is measured as a function of the wavelength. The spectrum is compared with a data bank of mineral pigment spectra. The comparison allows to identify pigments and, moreover, to deduce the surface state of the painting layer. Examples of Egyptian and modern paintings will be presented.

Frequently, it is desired to preserve the original tones of copper, brass and bronze surfaces which are used in decorative areas. This can be achieved by applying clear protective coatings, acting as weather barriers and surface protections against mechanical aggressions. The performance of two clear coatings and a hard coating is evaluated, using a linear scratch test and abrasion tests. The hybrid sol-gel coating greatly improves the wear resistance of brass. The corrosion-resistant varnish tested has very poor wear resistance. Too thin and porous hard-coating layers have poor corrosion and abrasion resistance. The hybrid sol-gel coating gives the best compromise in terms of aspect, properties and cost.

Raman microspectrometry is particularly suitable for the study of artefacts surface. This article outlines the advantages of this vibrational technique. Its capability for identification is illustrated by applications on wall paintings and dyed textiles, and their historical implications are mentioned.

Laser irradiation may alter the colour of certain pigments used in artworks. Owing to the increasing use of lasers in artwork conservation, this problem becomes extremely crucial especially in the case of a polychromy covered by environmental encrustation. X-ray diffraction analysis and optical microscopy were used to study the crystalline structure of selected irradiated pigments in order to identify the changes that take place upon laser irradiation. Two representative pigments were studied, cinnabar (HgS) and lead white (Pb(OH)2 2PbCO3). The results revealed a change in the crystalline phase or chemical composition, respectively, which can be barely detected owing to its superficial character, which is of a sub-micrometer scale.

This article presents research results obtained in the 4th framework (1994-1998) of the Standards, Measurements and Testing (SM& T) Program of the European Union, DG XII: the IMMACO project (Improvement of Means of Measurements on Archaeological Copper Alloys for characterization and Conservation). One of the aims of this project was to study copper alloy compositions of European objects dating from the Bronze Age to Roman times. This work has revealed that five types of alloys seem to be particularly representative of what was produced in these countries during this period. These alloy compositions will be certified as reference materials by the European Union. In the second part, artificial patinas have been made on the different bronze alloys using electrochemical polarizations as surface modification techniques. The characterization of the corrosion surfaces and interfaces formed during the treatment with "light microscopy" (LM) and scanning electron microscopy (SEM/EDX, X-Ray maping) have shown that the artificial patinas seem to be very close to those from excavations. As a consequence, the patined samples can be used as a substitute for genuine artifacts in the future to improve conservations techniques.

The restoration and preservation of metallic archaeological objects made of ferrous materials require the elimination of the chlorinated components contained in the corrosion products. Otherwise, after excavation of the artefact, corrosion will continue, sometimes at an accelerated rate. Different treatments may be applied for that purpose: electrolytic or alkaline sulphite baths, cold hydrogen plasma. This paper describes the hydrogen plasma treatment reactor in use at the Archaeological Museum of "Val d'Oise" , in France. Results of plasma treatments on artefacts are presented, together with optical measurements made at the reactor during the treatments.

This paper aims to show different ways the original surface of archaeological metal artifacts can be preserved in the corrosion products. Depending on the corrosion mechanism, the original surface can be located thanks to some features used as clues: remains of metallurgical structure fossilized in the corrosion products, content of elements either coming from the soil or from the original alloy, cleavage occurring at some corrosion interface. Moreover, some of the features of the corrosion layers can be compared to what happens at the very beginning of the corrosion, despite a relative gap in knowledge regarding the very long-term corrosion mechanisms.