Losset 1938.9734 Technical Analysis

Length 60 cm, Width 34.5 cm, Depth 9.6 cm

Multispectral Imaging

The object is described in the museum notes as being made from ash, although it is unclear how this analysis was made. The large vessels, visible to the naked eye, in the end grain of the wood in the images above do not contradict this conclusion. The individual vessels can be seen in the light coloured wood that marks the beginning of each growth ring. The large holes present throughout the wood in this image are likely too large to be vessels. The holes may have been caused by splitting in the wood along radially aligned, thin walled rows of cells visible in the microscopic reference image above. 

Wood Identification

While this object is identified in the museum notes as being made from Ash, 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 support the museum's analysis that the object is made of Ash (Fraxinus excelsior) wood. The wood is ring porous, there are tyloses present in the vessels, and the ray width is bi-or tri seriate.

 

FTIR spectral analysis showing comparison of sample collected from losset 1938.9734 (blue), and reference sample for Birch ( Betula pendula ) (red)

FTIR spectral analysis showing comparison of sample collected from losset 1938.9734 (blue), and reference sample for Birch (Betula pendula) (red)

FTIR Analysis

The sample of wood collected from losset 1938.9734 was analysed using Fourier Transform Infrared Spectroscopy (FTIR). The spectral analysis above compares the sample from losset 1969.678 with a reference sample for European Birch (Betula pendula) wood . 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.

While there are some minor variations in the intensity of some peaks, the spectrum for 1969.678 corresponds closely with that for Birch (Betula pendula) wood. There is no indication that the wood contains post-collection contaminants. 

 

Bibliography

L. Schoch, W., Heller, I., Schweingruber, FH, Kienast, F., 2004: Fraxinus excelsior L. Image. Wood anatomy of central European Species. 
Online version: www.woodanatomy.ch accessed 06.03.18