organic residues

Science of the Staffordshire Hoard

My name is Peter Mc Elhinney, and I am the organic materials specialist for the 7th Century Anglo-Saxon Staffordshire Hoard research project. The predominant imagery of the Staffordshire Hoard for many museum visitors is one of gold, garnets and other precious materials. While these materials make up a large proportion of the hoard objects, a small amount of organic materials have survived in the burial environment. Over the past few months I have been using different analytical techniques to better understand the nature of the organic components of the Staffordshire Hoard objects.

Materials like wood, horn, beeswax, animal glue, and calcium carbonate based fillers were employed structurally and decoratively in some hoard objects. Many of these materials would not have been visible when the objects were originally in use, but the nature in which the decorative elements were removed from their host substrates prior to burial exposed these materials, giving our research team extremely privileged access to samples for analysis.

Over the past few days, I have been analysing a large piece of beeswax that appears to have been used as a fill material for the beautiful pommel cap pictured here.

The front of the reconstructed sword pommel (c) Birmingham Museums Trust

The front of the reconstructed sword pommel (c) Birmingham Museums Trust

The analysis involved using Fourier Transform Infrared Spectroscopy (FTIR) to characterize the unknown material. In this case the sample was analysed across 16 different places, forming a grid of analysis points as shown in the image below.

Image View

The analysis revealed that beeswax was present at almost all of the 16 analysis points, and an additional protein based material was present at three analysis points.  The section highlighted in blue in the spectra below spans a region in which two protein related absorbance peaks appear. These peaks are known as the amide I and amide II bands, and are typically a good indicator that a sample contains some protein based material.

Spectra

In order to understand the distribution of the protein material across the sample I used the chemical mapping feature of the analysis software to produce the distribution map pictured below.

Chemical Imaging

The map shows the relative distribution of amide I and amide II bands (and therefore the protein content) across the surface of the wax sample. We can see from the map that there is a concentration of protein based material in the lower left hand corner of the map, as indicated by the warmer colours in this region. The map gives some indication that the protein based material is not evenly mixed through the beeswax sample, asking questions about how the fill material was mixed and applied.

Further analysis is required to determine the exact nature of the protein based material, but it may be animal glue which has been added to the molten wax, or possibly propolis or other impurities related to the original hive from which the wax was collected. I’ll be doing more analysis in the weeks ahead to solve this mystery.