Michael Attas

Visualization of cutaneous hemoglobin oxygenation and skin hydration using near-infrared spectroscopic imaging.

Background/aims: The visualization of skin hemodynamics and tissue water content has important implications in a number of areas of dermatology, plastic surgery, and clinical skin evaluation. The aim of this study was to develop instrumentation and techniques for infrared spectroscopic imaging, and to evaluate whether they can be used to make objective assessments of skin health, perhaps even before clinical signs are evident.

Near-infrared spectroscopic imaging in art conservation: investigation of drawing constituents

AbstractThe remote-sensing technique of spectroscopic imaging has been adapted to the non-destructive examination of works of art.The principleof near-infrared reflectance spectroscopic imaging is explained, and our instrumentation for art examination described. The technique allowsthe art materials to be distinguished by their composition, and under-drawings revealed. The initial results indicate that even over limitedwavelength ranges (650–1040 nm) and with relatively coarse spectral resolution (10 nm) a number of pigments can be distinguished on thebasis of variations in spectral properties such as spectral slope and the presence or absence of absorption bands. Software adapted from theremote-sensing image-processing field has been used to successfully map areas of different brown and black pigments across a drawing.Non-destructive identification of pigments can be used to address issues of attribution, age dating, and conservation.An additional advantageof this technique is that it can be performed off-site using portable instrumentation, and under relatively benign lighting conditions. Thetechnique has been applied to the examination of a 15th-century drawing,Untitled (The Holy Trinity), in the collection of the Winnipeg ArtGallery. Multivariate image analysis produced a set of principal component (PC) images highlighting different materials’ aspects of thedrawing. A color composite image produced from the PC images provided a direct visualization of the compositional characteristics of thework. Features of the under-drawing have been exposed, and its material tentatively identified as charcoal, by comparison with reference data.© 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Near infrared spectroscopic reflectance imaging: a new tool in art conservation

The application of infrared spectroscopic imaging to non-destructive examination of works of art is described. Its advantages over infrared photography and reflectography are discussed, in particular its ability to provide spectroscopic information, which potentially allows identification of pigments, binders, and other materials. Near-infrared spectra of a selection of brown and black pigments are presented. Results are given of the application of infrared spectroscopic imaging to two works of art in different media: an ink drawing and an oil painting.

Long-wavelength near-infrared spectroscopic imaging for in-vivo skin hydration measurements

A digital imaging system has been developed to collect skin hydration data. The system combines a near-infrared camera with a liquid-crystal tunable filter (LCTF) to acquire spectral images at multiple narrow wavelength bands between 960 and 1700 nm. Software has been developed to control the instrument and to process the data. Reflectance images were collected of subjects whose forearms had been treated to increase and decrease skin moisture. The infrared absorption band between 1400 and 1500 nm was used to calculate relative skin moisture, and the intensity of this band was plotted as a function of position in the form of a grayscale image. This is a rapid, non-contact and non-invasive technique to provide information on skin hydration of use to medical and cosmetic research and clinical practice.

Spectroscopic Studies on the Darkening of Lead White

Lead white is an historically important paint used by artists since antiquity. The darkening of lead white has been well documented in works of art such as paintings. In this paper, mid-infrared (MIR) and visible spectroscopy were used to examine spectral changes accompanying the darkening of lead white paint as a result of exposure to H2S(g). Laboratory-prepared paint and a commercial lead white paint were used to observe the darkening reaction overtime. Structural changes to the pigment, 2PbCO3Pb(OH)2, in lead white were readily detected using MIR by applying a thin film on a KBr pellet. Spectral changes at 3541 (O–H stretch), 1400 (C–O), and 680 cm−1 (C–O) were the most significant over time as the paint darkened. Visible spectra were also collected to provide a semi-quantitative measure of color change with structural changes observed by MIR. Experiments in the visible region were also conducted to compare the spectral response as % reflected and % transmitted light as lead white darkened. The effect of different binding agents (egg tempera, linseed oil, water, and gum Arabic) on the rate of darkening of lead white was also examined. Other sulfur-containing pigments such as orpiment and realgar were also tested for their ability to darken lead white. By applying paint as a thin film inside a sealed cuvette, darkening of lead white was observed in the visible spectra (800 nm) when either powdered orpiment or realgar was in placed in the cuvette for 24 h.

Pigment identification in artwork using graphite furnace atomic absorption spectrometry.

The use of a sampling technique is described for the identification of metals from inorganic pigments in paint. The sampling technique involves gently contacting a cotton swab with the painted surface to physically remove a minute quantity ( approximately 1-2mug) of pigment. The amount of material removed from the painted surface is invisible to the unaided eye and does not cause any visible effect to the painted surface. The cotton swab was then placed in a 1.5ml polystyrene beaker containing HNO(3) to extract pigment metals prior to analysis using graphite furnace atomic absorption spectrometry (GFAAS). GFAAS is well suited for identifying pigment metals since it requires small samples and many pigments consist of main group elements (e.g. Al) as well as transition metals (e.g. Zn, Fe and Cd). Using Cd (cadmium red) as the test element, the reproducibility of sampling a paint surface with the cotton swab was approximately 13% in either a water or oil medium. To test the feasibility of cotton sampling for pigment identification, samples were obtained from paintings (watercolour and oil) of a local collection. Raman spectra provided complementary information to the GFAAS, which together are essential for positive identification of some pigments. For example, GFAAS indicated the presence of Cu, but the Raman spectra positively identified the modern copper pigment phthalocyanine green (Cu(C(32)Cl(16)N(8)). Both Raman spectroscopy and GFAAS were useful for identifying ZnO as a white pigment.