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In humid air, copper and its high copper alloys (bronze) tend to form an oxide layer (patina). Natural patinas protect copper and its alloys from further corrosion processes. On the other hand, artists have frequently deliberately patinated bronze for visual effects. Thus, it is of great importance to study the patina changing mechanism to follow its chemical changes and to predict in advance the likely corrosion processes. Green chloride and green nitrate patinas, applied over the brown artist's patina, were tested, and also brown patina and the patina that develops on bare bronze. The Raman spectra were studied after chemical patination, and after exposing the patina samples in a climatic chamber, which can produce an environment that resembles an industrial atmosphere, for 12 weeks. The structures of the patinas and of the corrosion products were characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Cuprite and cuprous sulfite were found on the brown patina, atacamite on the green chloride patina, and a mixture of gerhardite and rouaite on the blue to green nitrate type patina. After 12 weeks of exposure to humidity, a controlled concentration of SO 2 , and salt spray mist, the corrosion products changed. In general, clinoatacamite and paratacamite are the end corrosion products, after an intermediate brochantite stage on the green chloride and green nitrate type patinas. The end products of each patina type are given.

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The colorants and additives present in lithographic inks used in a group of posters manufactured during the period between 1890 and 1920, an extremely fruitful period regarding the development of the synthetic dye and pigment industry, were identified by Raman spectroscopy. Synthetic organic pigments and dyes were detected along with inorganic pigments. Red, blue and yellow synthetic organic pigments were more frequently observed in posters manufactured by the end of the 1890-1920 period, reflecting that lithographers were actively experimenting to achieve hues not accessible using inorganic pigments alone. The water-sensitivity of the inks containing synthetic organic colorants is discussed in relation to the potential application of aqueous conservation treatments to early posters.

Raman mapping can provide molecular information to complement data derived from other analytical techniques in works of art and other objects of cultural significance. Raman mapping can be performed using a motorized microscope stage that moves a sample or an object point by point in two spatial directions. The method can be used both noninvasively in works of art that fit under a microscope objective and in microsamples when, for example, obtaining information on the samples' layering structure is necessary. This paper reports on the development of a Raman mapping approach based on a set of scanning mirrors that direct the laser beam in two spatial directions, vertically through the microscope head or through a horizontal exit on the Raman microspectrometer. The first configuration still has limitations in terms of the size of the work of art that can be analyzed, as it has to fit under the microscope objective, but considerably larger objects can be studied when using the scanning mirrors placed in the horizontal exit. In this paper, the advantages and limitations of these two Raman mapping approaches are compared and discussed on the basis of an example of a contemporary oil painting on canvas. Copyright © 2010 John Wiley & Sons, Ltd.

In the present work, a new substrate is proposed for the surface‐enhanced Raman spectroscopy (SERS) analysis of samples, which are of cultural heritage importance. A new and simple procedure is presented for the preparation of a stable SERS‐active substrate. It is based on the photoreduction of silver nitrate by ultraviolet light utilising hydroxypropyl cellulose as stabilising agent. The substrate's characteristics were tested and compared with a known substrate: a citrate‐reduced silver colloid, with alizarin as a reference material. Using the new substrate, it was possible to positively detect the organic dye alizarin red S, and two organic pigments: madder lake and alizarin crimson dark, as well as organic colourants prepared in paint layers with different organic binders without an interfering signal arising from the media, and without sample pre‐treatment. Furthermore, the investigated substrate also shows promising characteristics for the analysis of the cross sections of the samples because of its viscosity and the possibility of maintaining better control of the application of the substrate to the layer of interest. Copyright © 2014 John Wiley & Sons, Ltd.

Patinas form spontaneously on copper and high copper alloys when exposed to humidity and air. They usually protect the underlying metal from corrosion. Bronze is often chemically patinated by artists to achieve an antique appearance. However, in the case of chemical patinations on bronze, there is a lack of studies about their change over time during exposure to different types of environments.Recent types of bronze, brown patina and two green type patinas (green chloride and green nitrate patina) applied over a brown patina, were selected for testing. The aim of the present study was to monitor the transformation process of chemically formed patinas and of the bronze itself after exposure to simulated urban acid rain, for a period of 35 days. The structures of the patina and corrosion products were characterized by scanning electron microscopy (SEM) and Raman spectroscopy.Three differently coloured patinas were scraped off from the bronze statue of the poet France Pre seren, two green type patinas and one brown type, to predict the probable influences of the environment, the base alloy and previously used patination techniques.The relative intensities measured on the chloride-type patina are marked as follows: vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder.Raman investigation of artificial patinas on recent bronze

X-ray diffraction (XRD) complemented by Raman spectroscopy analyses of synthetic organic pigments in powder samples, layered paint systems, and commercial artists’ paints bound in acrylic, alkyd, and oil media are presented. The potential and limitations of the techniques to identify and characterize mixtures of these pigments, along with inorganic extenders, in works of art are exemplified and discussed. Stratified model paint systems that mimic the layering structure typically found in modern paintings are used to evaluate the effect of the μXRD experimental parameters, as well as extenders or fillers commonly found in modern artists’ paint formulations, on the quality of the patterns recorded in microsamples of paint. XRD is demonstrated for the first time to be an effective tool for the specific identification of synthetic organic pigment mixtures and fillers in acrylic and alkyd bound artists’ paints, while the identification of these pigments by XRD in oil bound paints appears problematic. Detailed crystallographic information provided by XRD is shown to be complementary to molecular information provided by Raman analysis. The combined use of these techniques allows for more frequent unambiguous compound identification than would be possible using one technique alone.