Wax Seals – Material and Context
An Interdisciplinary Research Project
Elke Cwiertnia, Adrian Ailes, Paul Dryburgh
The National Archives, UK, holds many thousands of wax seal impressions – the largest collection of these important historical objects in the United Kingdom. This vast collection has not before been examined explicitly with regard to sealing material and techniques. Details about their production, therefore, are relatively unknown and a comparison of their materiality has not yet been possible.
Wax seals attached to charters and letters were a primary means of authentication and communication in the Middle Ages. The project ‘Wax Seals: Material and Context’ at The National Archives, from February 2014 to August 2015, investigated their materiality, manufacture, use, and application techniques.
During the project, historians and seals specialists were involved in developing routes of investigation to complex historical questions that might be answered by examining the materiality of wax seals. Key research questions prompting the technical analysis included: how is the sealing wax made and by whom; where does the wax come from; can greater knowledge of the wax composition of seals aid conservation work or contextualisation; do different departments in government, such as the Exchequer and Chancery, or different members of the ruling family, buy the same wax; is the colour, size and quality of a seal important? At the same time it was agreed that the results themselves should be allowed to prompt new questions and suggest new areas of investigation.
The research questions were arranged in work packages (sub-projects) and considered by an interdisciplinary team composed of specialist staff from the Collection Care Department (CCD) and the Advice and Records Knowledge Department (ARK) at the Archives.
[CCD: Elke Cwiertnia, Nancy Bell and Kostas Ntanos; ARK: Paul Dryburgh and Adrian Ailes] Figure 1 provides an overview of the responsibilities of the different experts and the main connections between each discipline.
Fig. 1 Experts and their responsibilities
This interdisciplinary project used scientific studies in the form of visual examination and material analysis of selected wax seals and documentary evidence to gain valuable insights into the making and meaning of these objects [polarised light microscopy (PLM), cross sections, Gas Chromatography Mass Spectrometry (GC-MS), pyrolysis gas chromatography mass spectrometry (PyGC-MS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray florescence spectrometry (XRF), Fourier transform infrared spectroscopy (FTIR)].
The main outcomes and findings reflect the interesting journey while examining about 70 wax seals in the collection of The National Archives:
- An interdisciplinary research group working within TNA was established.
- A new, more accurate method to measure wax seals was developed.
- Details and developments about the materials used in seals, including beeswax, coniferous resin, vermilion and verdigris were identified, for example: pigment content (and therefore material costs) in Canterbury seals (and possibly other seals) decrease over time
- Historical sources emphasised the importance of wax as a key commodity to central government and its import from other countries, mainly through the Baltic Sea and certain European cities. Vermilion was likely to be imported from Spain.
- Size (diameter, depth and relief) of the Great Seals from 1100 to 1300 increases.
- Certain green and red seals change colour over time (to a brown appearance).
- Green wax can be prepared using beeswax and a green pigment or cooking beeswax in a copper vessel.
- Cords on the great seals are usually made of coloured silk. Colour, braiding and knotting technique might have/hide a meaning. Cords were found to run at an angle through seals (particularly early double-sided seals) presumably to accommodate the lugs of the matrices.
It also has created new questions relating to the materiality of the documents, and allowed us to use our developed examination methods.
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Fig. 2 a and b: Henry of Lancaster’s seal (front) detached from Barons’ Letter B, 1301 (catalogue reference: E 26/1 Cord E)
Fig. 3: X–ray fluorescence (XRF) analysis on a wax seal to investigate the elements (which helps to identify the pigments used)
Fig. 4: Verdigris (green pigment) in beeswax, after artificial ageing for 3 weeks (colour change on the edges of the pigment)
Fig. 5: Reproduction of sealing wax mixture, here: verdigris (green pigment) in beeswax, colour changes due to heating for several hours