PIMA Spectroscopy PIMA PROJECT

What does PIMA stand for?

PIMA stands for Portable Infrared Mineral Analyzer.

How does the PIMA work?

The PIMA has a small ‘window’ that is placed against the flat surface of a sample.  The instrument takes between 30-60 seconds to ‘read’ the sample.  The PIMA uses the short wavelength infrared (SWIR) portion of the electromagnetic spectrum (from 1300-2500 nanometers) and measures the unaborbed (reflected) radiation bounced back from a sample's surface. PIMA spectroscopy reveals the interatomic bond energies characteristic of specific minerals.    The technique is useful for determining degree of crystallinity of a material.

By looking at the position, depth and shape of the absorption features, an experienced spectroscopist can determine which minerals are present in the sample.  PIMA software provides automatic comparison of spectra with reference databases created by the Australian manufactures. Analysts can also create their own reference databases using local minerals as controls.

What kinds of materials can be analyzed with PIMA?

The best materials for PIMA analysis contain hydroxyls (OH groups), such as phyllosilicates (including clay, chlorite, and serpentine minerals, hydroxylated silicates (epidotes and amphiboles), sulphates (eg. gypsum), and carbonates.  The PIMA has been used to analyze minerals by geologists and the mining industry in Australia, Canada, Europe, and North and South America.  It has recently been applied to archaeological artifacts of stone and clay such as Hopewell pipes and Cahokian-style flint clay figurines (see Emerson et al. 2002, 2003; Emerson and Hughes 2000, 2001; Hughes et al. 1998; Wisseman et al. 2002).  By taking samples of stone and clay raw material sources in the Midwest, a reference database of spectra is being compiled for comparison with artifact spectra.

PIMA can also be used to study soils and sediments from archaeological sites. Its applicability to bone analysis is also now being explored (see an abstact to a conference paper given by Linda Klepinger and Sarah Wisseman).

The applicability to ceramics is uncertain.  High-fired ceramics are dehydrated, and thus do not produce good spectra using PIMA.  Low-fired ceramics (fired to less than 800 degrees centigrade) do produce useable spectra. However, ceramics tend to be heterogeneous , with mixed clays and inclusions--temper-- that will also be 'read' by the PIMA. It is possible to factor out some minerals from a spectra, leaving behind the mineral signature of the clay, but this has yet to be explored fully.

PIMA has been very successful in determining the mineral composition of museum artifacts.  It has proven useful in museum curation and determination of fakes or reconstructed parts of museum pieces.  PIMA's greatest advantage is that it is non-destructive, so accurate readings can be taken without moving or sampling the object.   (see an upcoming article in the Journal of the American Institute for Conservation, by Wisseman, Emerson, Hynes, and Hughes: Using a Portable Spectrometer to Source Archaeological Materials and to Detect Restorations in Museum Objects)

What are the advantages of using the PIMA?

The PIMA has three major advantages:
            1) It’s portable - PIMA can be used in the field or in a museum setting.  It has a palmtop computer that stores readings, or it can be hooked up to a laptop for instant spectral output.
            2) It’s fast and easy to operate- PIMA readings take 30-60 seconds.  In addition, there is no sample preparation involved.
            3) It’s totally non-destructive - Readings can be taken from any reasonable flat surface.   This is especially important for museum pieces and archaeological artifacts.

How does PIMA compare to other mineralogical and chemical analyses such as thin-section petrography, X-ray diffraction (XRD), X-ray fluorescence (XRF), instrumental neutron activation analysis (INAA), and sequential acid dissolution-inductively coupled plasma (SDA-ICP)?

The PIMA spectrometer is almost unique in its portability and non-destructive operation.   PIMA is a semi-quantitative mineraological technique like XRD. It does not provide quantitative, multielemental data like INAA or XRF.

For sourcing archaeological materials, a combined method that uses portable PIMA in conjunction with another laboratory method produces the best results.  PIMA serves as a non-destructive first step in analyzing mineral composition.  It can help researchers select which samples should be further analyzed using more traditional laboratory-based techniques. This approach saves time, money, and the samples themselves from unnecessary destruction.

Copyright 2003. University of Illinois at Urbana-Champaign.