Chemical Analysis of Historical Materials and Cultural Heritage Objects
Activities
Analysis of Sediments on Medieval Vessels
Large quantities of pottery vessels were produced in the Middle Ages. Those were used for most of the housework. Chemical analysis can help archaeologist to better understanding of everyday life in the Middle Ages. We are able to identify age of the vessels, but also their purpose, as we are able to analyse sediments inside the vessels.
Suitable method for organic sediment analysis is an infrared spectroscopy. On figure (Fig. 7) and (Fig. 8) you can see a sampling for analysis. In three tested samples proteins were detected. This is evidence that food was stored in vessels that were used probably in the kitchen.
In the sample form vessel 658, (Fig. 9 and Fig. 10), we identified pine resin. It is proved by comparing the spectra of our sample (spectrum A) with pine resin spectrum (spectrum E). The sample however contains other chemical compounds, as is clear from a comparison of our sample spectrum with calcium phosphate spectrum (B), silicon dioxide spectrum (C) and calcium sulphate spectrum (D) (Fig. 11). We can conclude that this vessel was used for melting a resin that was probably used for making torches.
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11 Spectrum (A) of the sample No.11 from ceramic vessel 658, demonstrate a presence of a pine resin, compare with the spectrum (E) of pure pine resin. On both spectra is identical absorption band with a peak at wavenumber 2930 cm-1.
Treatment of the Archaeological Findings of the Celtic Head Sculpture
One of the most important archaeological discoveries in the Czech region, from the period around half of the 2nd century BC, is the stone sculpture of the
Celtic hero head (Fig. 12). The area north of the Alps was inhabited by Celtic tribes in that era. Pieces of the stone head were found accidentally by local residents in the fields in central Bohemia, at Msenecke Zehrovice near the city Slany in 1943. After the war, the head was restored and the rare finding was exhibited in National Museum. In 2009, the sculpture was lent to the exhibition
Art of the Celts in the Historical Museum in Bern.
Due to transfer to another setting was therefore important to determine what material was used to glue individual parts together and whether the sculpture surface was treated. Infrared spectroscopy was used as a suitable method. Miniature pieces were therefore extracted from the back of the head (Fig. 13).
Fig. 12 Celtic head sculpture from the front.
Fig. 13 Back of the Celtic head sculpture and two sampling points.
Fig. 14 (A) Spectrum of the sample from point 1, (B) spectrum of gypsum plaster (C) spectrum of beeswax.
Fig. 15 (A) Spectrum of the sample from point 2, Comparative spectra: (B) calcium stearate, (C) polyacrylate resin, (D) calcium sulphate dihydrate (gypsum plaster), (E) alpha silica.
By a comparison of the sample spectrum and comparative spectra of pure substances, we can confirm that as an adhesion of individual parts of the sculpture the mixture of gypsum plaster (peak 1695 and 1619 cm-1) and acrylic resin (peak 1732 cm-1) was used and that the surface of the head was treated with beeswax. Identical absorption band with a peak at wavenumber 2917 cm-1 and 2851 cm-1.
