Losset 67.1947 Technical Analysis

Length 73 cm, Width 53 cm, Depth 6cm

Multispectral Imaging 

Infra-red imaging of losset 67.1947 highlighted the presence of large rays in the wood. Oak has some of the largest rays of any native Irish wood species (visible as dark 'flecks' in the wood), and their presence in this object is consistent with a prior wood species identification for this object (Scannell, 1980). 

 

Wood Identification

A small sample of wood was collected from the underside of losset 67.1947 (see annotation 1 on the model above). This object was carved from a large tree trunk, with the long axis of the object aligned with the longitudinal axis of the tree.  Given the orientation of the object in relation to the tree trunk from which it is formed, the sample was collected from a region of wood that contains some of the 'newest' growth rings available for this object. In addition, as the sample location corresponds with a split in the wood on the underside of the object, collecting the sample from this region has minimised the visual disruption to the object. 

A sub-sample was cut into thin slices known as 'sections', and mounted for examination using a scanning electron microscope (SEM). The scanning electron microscope can resolve microscopic features in the wood that  help to identify the particular species of tree that the losset was made from.

Prior wood identification carried out for this object (Scannel 1980) concluded that it was made from oak (Quercus). Oak wood rays range in width from unisereate to up to 30 cells wide, and these larger rays are typically visible with the naked eye, appearing as dark ‘flecks’ on the wood surface (Appendix 1). The prominent rays visible in the macro documentation images and highlighted in the reflected infrared images above support the prior wood species identification.

The debris like material visible within the vessel members in the images above are known as tyloses; outgrowths that help the living tree to manage stresses associated with drought or infection (Pallardy 2010: 67). These are found in only four native Irish tree species- ash (Fraxinus excelsior), elder (Sambucus nigra), elm (Ulmus glabra), and oak (Quercus robur) (see Appendix 1). The rays in ash, elder, and elm range in width from 2-5 cells wide, and would not be as prominent as those visible in this object. This confirms that the wood used to produce losset 67.1947 is oak (Quercus robur).

 

FTIR spectral analysis showing comparison of sample collected from losset 67.1947 (blue), a reference sample for Birch ( Betula pendula ) (red), and a reference sample for natural gypsum (green).

FTIR spectral analysis showing comparison of sample collected from losset 67.1947 (blue), a reference sample for Birch (Betula pendula) (red), and a reference sample for natural gypsum (green).

FTIR Analysis

The sample of wood collected from spade 67.1947 was analysed using Fourier Transform Infrared Spectroscopy (FTIR). The spectral analysis above compares the sample from spade 67.1947 with a reference sample for European Birch wood (Betula pendula), and a sample for natural gypsum.

The FTIR spectrum for the wood sample collected from losses 67.1947 is broadly comparable with that of a Quercus robur reference spectrum (excluding the potential post-collection contaminant described below). Variations between the the archaeological and reference wood spectra relate primarily to the amount of bound water in the samples from which the spectra are derived, and to deterioration or loss of some of the main polymeric components; hemicellulose and lignin. 

The increased intensity of the peak centred around 3340cm-1 on the spectrum for oak relates to O-H stretching vibrations, and is due to the increased volume of bound water in the unseasoned sample of oak wood used to produce the reference spectra. The peak at 1732cm-1 visible in the oak reference spectrum but not in spectrum 67.1947.1 is assigned to unconjugated C=O stretching vibrations in the hemicellulose xylan (Pandey and Pitman 2003: 154; Genestar and Palou 2006: 988; Emandi et al. 2011: 581). The reduced intensity of the band, visible only as a subtle shoulder in the archaeological wood spectrum, suggests a deterioration of the hemicellulose component of the wood on losses 67.1947.

A band centred around 1240 cm-1 in the oak wood reference spectrum appears as two separate peaks at 1266 cm−1 and 1222cm-1 in spectrum 67.1947.1. This may be due to a decrease in the intensity of the band at 1240cm-1 as shown in the wood reference spectra, resulting from xylan degradation, as this band results partially from C–O vibrations in xylan. (Pandey and Pitman 2003: 154). The reduced intensity of the peak for C=O stretching vibrations in xylan between 1736-1724 cm-1, supports this conclusion.

There are a number of sharp peaks between 2970 and 2840 cm-1, and at 1458 and 1377 cm-1 for the spectrum form losset 67.1947 that do not appear in the oak reference spectrum. These peaks relate to C-H stretching vibrations, and their presence indicates that the wood contains an alkane based contaminant. While the collection treatment history for objects from the Armagh County Museum is not fully documented, it is possible that the object has been treated with a petrochemical based preservative, and a strong chemical smell was noted when examining this object. Wood preservation treatments using petroleum are noted as being in use in Europe in the early 20th century (Unger et al. 2001:4), despite their value as pesticides being called into question. The reference spectrum for kerosene, which consists predominantly of C6H14 (Mohammadian et al. 2013: 235) is shown here for purposes of comparison. 

SEM EDX Analysis

While the major elements detected were carbon and oxygen (both constituents of the major organic polymers in wood), the presence of localised concentrations of calcium, silicon, and iron at site of interest two, visible as bright white spots on the upper right hand corner of the electron image, might suggest mineral deposits from the burial environment. Alternatively, given the sample location on the underside of the losset, these localised concentrations may relate to dirt or grit that became embedded in the wood on the underside of the object during use.  

The co-deposition of calcium and oxygen visible in the sample might also indicate calcium oxalate [CaC2O4(H2O)] crystals in this area; a by-product of fungal deterioration of wood (Genestar and Palou 2006: 988; Genestar and Pons 2007: 333,337). The presence of trace amounts of chlorine and potassium in the sample may relate to the object burial conditions. 

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Radiocarbon Dating

Losset 67.1947 was radio carbon dated to 746 ± 26 BP. Calibration using the IntCal13 calibration curve (Reimer et al. 2013) returned a discrete range of 727-662 calBP (95.4%), which translates to a production date range of A.D. 1223-1288. 


The sample location for this object was not collected from the ‘newest’ wood growth for this object, but from wood produced at an earlier time. A calculation based on the projected longitudinally aligned orientation of the object within the living tree from which it was carved, the object maximum width (57cm), and an approximated growth rate of 1.5-2 cm circumference per year (RFS 2015), indicate that it was possible to carve the losset from a 90-120 year old oak tree. Assuming that the losset was carved from a tree of approximate diameter to the object widest point, the date of production for the object could exceed the stated radiocarbon date range by approximately 100 years

Bibliography

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Schoch, W., Heller, I., Schweingruber, FH, Kienast, F. (2004) Wood anatomy of central European Species. Online version: http://www.woodanatomy.ch/species.php?code=QURO accessed 22.01.19

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