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CCI provides chemical analysis for Canadian cultural and heritage institutions to support conservation treatments, documentation and authentication, and historical research. Until 1996 infrared (IR) spectroscopic analyses were always done in our laboratories in Ottawa — which required either that objects be sent to Ottawa, or that samples be taken from objects in their home locations and sent to the lab. Our mobile, on-site IR spectroscopic analysis service can eliminate the dangers of transporting objects, and allow many objects from a collection to be analysed rather than just a few.
Innovative IR spectroscopic techniques, including diamond cell sampling devices, IR microspectroscopy, and IR thermal microscopy, have been mainstays of analysis at CCI since its earliest days of operation. Recently purchased state-of-the-art spectrometers and IR microscopes allow us to continue providing this service. But these techniques are tied to large equipment in the laboratory, and require that objects or samples be sent to Ottawa. Therefore, now we also offer a mobile IR spectroscopic analytical service. In addition to on-site chemical analysis, this service provides an opportunity for several days of direct contact and discussion between CCI and museum personnel.
It must be noted that analysis using portable mobile spectrometers is not as complete as that performed in an analytical laboratory. However, for many basic questions about chemical composition, the mobile equipment is fully satisfactory. If more detailed analysis is necessary, then samples or objects can be sent to the lab. And the information provided by mobile spectrometers enables much better informed choices of objects, sample locations, and types to be made.
CCI currently uses two portable IR spectrometers with different modes of analysis.
Fibre optic probe spectrometer
Our first portable spectrometer, acquired in 1995, uses a fibre optic probe (FOP) attached to the spectrometer to acquire fibre optic reflection spectra (Figure 1). This technique is completely non-contact and non-destructive. It allows objects to be analysed without moving them from their place of display or storage, and without taking samples (Figure 2). The FOP is placed about 2–4 mm from the surface of the object in a perpendicular attitude. IR radiation from the source travels down the probe to the object, is reflected from the object back up into the probe, and directed to the detector. Because the object absorbs some radiation from the incident beam, interpreting the recorded spectrum of the reflected radiation allows the chemical composition of the object to be determined.
The FOP is about 80 cm long, so any spot on the surface of an object within that distance from the spectrometer can be analysed. The components of the spectrometer are small enough that they can be mounted on stands, lifts, or gantries, which allows the spectrometer and FOP to be easily positioned for analysis (Figure 3). The spectrometer can also be placed on an XYZ translating carriage for mapping the composition of objects.
This spectrometer can be used to analyse any type of object with any composition (organic or inorganic), except metals. It is, however, constrained by the nature of the surface. Objects that are relatively flat with smooth surfaces have mirror-like reflection, which produces the best spectra and the most accurate results. Objects that have been successfully analysed include all sorts of natural and synthetic ethnographic beads, jewellery, costume accessories, toiletry articles, scientific and medical apparatus, and adhesives. These objects have been variously composed of natural materials such as bone, horn, and shell; inorganic materials such as minerals and glass; and organic materials such as plastics and resins. Under optimum conditions the technique is particularly well suited to analysis of composite objects made from many different materials.
TravelIR spectrometer
The TravelIR, acquired in 2001, is even smaller and more portable than the FOP spectrometer. It is based on the Attenuated Total Reflection (ATR) technique and, unlike the FOP spectrometer, requires direct contact with the object or sample being analysed (Figure 4). Spectra from the TravelIR are of much better quality than those from the FOP spectrometer, and therefore much easier to interpret. For this reason the TravelIR is used for analysis whenever possible.
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All types of objects, except metals, can be analysed by the TravelIR spectrometer. The outer 5-cm zone of flat materials like paper, parchment, and textiles, and objects that are small enough to be placed against the ATR crystal, can be analysed directly. For larger three-dimensional objects, tiny samples (<100 µm in diameter) must be taken and placed on the ATR crystal. Figure 5 shows the image of a hair on the ATR crystal and the spectrum obtained, which can be clearly identified as the protein expected for hair.
The spectroscopy arsenal has recently expanded to include a near-IR spectrometer with a FOP that will operate in the spectral range between IR and visible radiation. This technique is currently in development and should soon be available for incorporation into CCI’s suite of mobile on-site IR spectroscopic services.
In addition to portable IR spectroscopy, CCI also provides on-site analytical services for colorimetry and gloss measurement, which is particularly useful for colour matching and for monitoring fading due to environmental agents, as well as metals and inorganics analysis using portable X-ray fluorescence spectrometers. Since one limitation of IR spectroscopy (either technique) is that it cannot determine the identity of metals, the latter is a particularly useful complement to IR spectroscopy.
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