Trough 51.1935 Technical Analysis

Length 69 cm, Width 34 cm, Depth 24 cm

Multi-spectral Imaging

The infra-red and macro images above highlight dark coloured marks on the interior of trough 51.1935 consistent with scorching of the wood. These markings suggest that the object was used for hot stone cooking. In this technique stones heated in a nearby fire are added to a liquid within the vessel. The stones are continually retrieved, reheated, and returned to the liquid until it reaches the desired temperature. 

Wood Species Identification

While this object is identified as being made from Hazel (Scannell, 1980), the method of identification is unclear. A small sample of wood was collected from the underside of losset 1938.9734 (see annotation 1 on the model above) so that the initial identification could be confirmed. 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. The combination of features outlined in the SEM image descriptions above does not support the previous analysis that the object is made of Hazel (Corylus), and is more likely Alder (Alnus glutinosa) or Birch (Betula pendula) wood. The number of bars on the sclariform perforation plates of Hazel wood ranges from 5-10. Almost all of the sclariform perforation plates visible in the SEM images above exceed 10 in number.  

FTIR spectral analysis showing comparison of sample collected from trough 51.1935 (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 trough 51.1935 (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 trough 51.1935 was analysed using Fourier Transform Infrared Spectroscopy (FTIR). The spectral analysis above compares the sample from trough 51.1935 with a reference sample for European Birch wood (Betula pendula), and a reference sample for natural gypsum.

As the predominant component of plant fibres is cellulose, and other major constituents (hemicelluloses and pectins) are also polysaccharides, the FTIR spectra of different cellulosic plant materials are superficially similar and cannot be readily distinguished by eye. In addition, degradation of one or more components of the plant material e.g. through oxidation of the cellulose molecule, will influence the position and intensity of spectral peaks relative to non-deteriorated reference spectra.

There are, however, a number of fairly consistent spectral peaks indicative of cellulosic carbohydrate within a sample. The majority of cellulosic carbohydrates will exhibit a broad band from 3600–3100cm-1 arising from O-H stretching in bound or absorbed water. A broad band relating to C-H stretching from aromatic hydrocarbons at 3100-3300 cm-1 can be obscured or partially obscured by the broad O-H stretching band described previously. Additional peaks relating to the cellulose component of plant material include peaks for C-H stretching of methylene groups between 3000 and 2800cm-1, C-H deformation in cellulose and hemicellulose at 1371cm-1, C-H vibrations at 1319 cm-1, an intense peak at about 1030cm-1 relating to C-O bonding (this is typically a combined peak for cellulose and hemi-cellulose), and a shoulder at 897cm-1 relating to C-H bending. Additional shoulders at 1155cm-1 and 1105cm-1 on the C-O band at about 1030cm-1 relate to stretching and contraction (so called ‘breathing’) vibrations within the benzene rings, and glycosidic linkages between carbohydrate molecules respectively.

In addition to the peaks associated with wood, a number of addition peaks indicate the presence of CaSo4 (gypsum) in the sample. These include antisymmetric and symmetric O-H stretching bands between 3700 and 3200 cm-1, a strong SO4 stretching band between 1140 and 1080cm-1, and an SO4 bending band around 620cm-1 (Derrick et al. 1999)  As gypsum is a constituent of some types of Irish peat, it seems likely that it's presence here relates to minerals embedded into the object during use or burial.  

Bibliography

Derrick, M. R., Stulik, D. and Landry, J. M. (1999) Infrared Spectroscopy in Conservation Science. Getty Conservation Institute.

Scannell, M. (1980) Report on wooden trays, methers and other objects from Armagh Museum. Dublin: Department of Agriculture and Fisheries, Ireland.