The Wax Seal
A seal is used to authenticate a document such as charters and represent the owner’s portrait or coat of arms. (The National Archives, 2024). ​Medieval seals not only reflected the medieval culture and society from which they were made for, but they were created to represent truth as reality (Adams, N. Cherry, J. Robinson, J. 2008).
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Use the Reflectance Transformation Imaging (RTI) tool to inspect Henry III's wax seal.
Can you see him sitting upon his throne?
1259 to 1272 Second Seal from John Speed's 'Historie of Great Britaine' © Mernick
1450-1460 English seal matrix. © Victoria & Albert Museum 2009
How was it made?
To make a seal, wax is pressed into a seal-making device known as a matrix. The matrix was cut by specialist seal makers and engraved with a negative image.
To make a double sided seal, two matrixes would have been pressed together with a cake of wax in the centre. The matrix would be carefully removed to reveal a relief of the engraved image onto the surface of the wax (V&A, 2009).
X-ray Fluorescence. What's that?
X-ray Fluorescence (XRF) is a non-destructive analytical technique and provides good qualitative and quantitative results. The XRF analyser emits an x-ray into the sample, and a secondary fluorescent x-ray is emitted by the sample. With this, we can determine which elements are present and in what amounts (Shugar, A.N, Mass, J.L, 2013).
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However, XRF is only capable of measuring the elements found within the periodic table. This is useful for identifying the metals found within historical artefacts, but less effective for identifying non-metal compounds.
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Through XRF, we have been able to detect the presence of copper which is responsible for the original wax's green colouring.
Students carrying out XRF analysis of the wax seal.
Why is it green?
The practice of colouring wax seals began in the 12th century and was done to heighten the significance of a document by implying a visual ranking of the owner of the seal.
One of the main ways to produce green beeswax was to add green pigments like copper or Verdigris to the wax, or by heating the wax in a copper pan (Kasso, T.M., Enevold, R., Johns, S. et al 2023).
What else is in there?
From the late 12th century, resins and fillers were added to the beeswax to help strengthen the seal.
By using XRF analysis, we have identified the presence of calcium in the original green wax. Calcium carbonate, otherwise known as 'whiting' was used as a filler material to provide stability for the wax seal (Kasso, T.M., Enevold, R., Johns, S. et al 2023).
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Fourier Transform Infrared? That sounds complicated.
Fourier Transform Infrared (FTIR) spectroscopy is another non-destructive method of analysis. FTIR uses infrared radiation to measure the unique vibrational energies of molecules. By measuring the vibrations, we can identify the distinctive energies of solids, liquids and gasses. This technique allows for us to identify the non-metal compounds that XRF is unable to (Derrick, M. et al, 1999).
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However, this this form of analysis has some limitations. Results are less quantitative than XRF and don't provide the exact quantities of materials found within an object. Additionally, it can take time to build a reliable database resource. Often objects are made of a number of materials in varying quantities, and this can prove tricky for the conservator to identify the materials present when the artefact is composed of a mixture of substances.
1259 to 1272 Second Seal from John Speed's 'Historie of Great Britaine' © Mernick
Interpreting graphs. It can't be that hard, right?
Through FTIR analysis, we can observe that the new wax (orange) and the old wax (green) are composed of a different combination of materials.
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The known beeswax sample compares similarly to both results, and it could be interpreted that the observed difference is due to the presence of the calcium carbonate found within the original wax. ​The presence of the calcium carbonate has possibly caused the graph to "dip" in the middle (Derrick, M. et al, 1999).
FTIR graph results of original wax sample.
FTIR graph results of restoration wax sample.
FTIR graph sample of calcium carbonate. Derrick, M. et al, 1999
Multi-spectral Imaging (MSI)
Multi-spectral Imaging (MSI) is another form of non-destructive analysis that acquires images of an object using varying wavelength ranges. It captures image data from wavelengths beyond the visible light range, such as infrared (IR) and ultra-violet (UV).
Conservators can use MSI to visually enhance an artefact, and is often used to identify pigments and retouching on works of art (Cultural Heritage Science Open Source, 2024).
By using MSI, we have captured the 'fluoresce' emitted by the restoration wax. By comparing the colour to UV light colour databases, we can begin to conclude the wax identification.
The restoration wax fluoresces orange, which indicates that it is beeswax. Beeswax fluoresces orange under longwave UV light (Measday, D. et al, 2024). The original green wax does not emit any fluorescence however. This is likely due to the age of the sample, and the surface deterioration.
This type of interpretation is not an exact science and it is open to interpretation. It is therefore important that conservators use several types of identification methods to ensure that they can make accurate conclusions. ​
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