ANALYSIS OF AN ANGLO-SAXON LOZENGE-SHAPED BROOCH for Corinium Museum, Cirencester AsF Report: 0001.02 November 2012 (amended September 2013) www.smallfinds.org.uk ANALYSIS OF AN ANGLO-SAXON LOZENGE-SHAPED BROOCH Prepared for Corinium Museum, Cirencester Park Street Cirencester Glos. GL7 2BX by Jörn Schuster AsF Report: 0001.02 November 2012 (amended September 2013) Disclaimer: This document has been prepared for the titled project or named part thereof and should not be relied upon or used for any other project without an independent check being carried out as to its suitability and prior written authority of ARCHÆOLOGICALsmallFINDS being obtained. ARCHÆOLOGICALsmallFINDS accepts no responsibility or liability for the consequences of this document being used for a purpose other than the purposes for which it was commissioned. Any person/party using or relying on the document for such other purposes agrees, and will by such use or reliance be taken to confirm their agreement to indemnify ARCHÆOLOGICALsmallFINDS for all loss or damage resulting therefrom. ARCHÆOLOGICALsmallFINDS accepts no responsibility or liability for this document to any party other than the person/party by whom it was commissioned. © ARCHÆOLOGICALsmallFINDS 2012 all rights reserved T 01747 820216 E info@smallfinds.org.uk Analysis of an Anglo-Saxon lozenge-shaped brooch 1. Introduction ARCHÆOLOGICALsmallFINDS (AsF) was commissioned by Corinium Museum to provide a detailed description and analysis of a brooch acquired by the museum from a metal detectorist. The brooch (Figure 1) is an extraordinary specimen of a form of brooch that has only relatively recently been established as an Anglo-Saxon type, now commonly referred to as ‘safety-pin’ brooch (cf. PAS Find number: HAMP-CEBED7). Among this rare brooch type the flat bows usually take the form of narrow lozenges, elongated ovals or simply wires. The geometric chip-carved pattern on the remarkably large lozenge plate of this example is highly unusual, and together with the method of surface decoration as well as the attachment of the unilateral spring warranted further analysis. Figure 1. Anglo-Saxon lozenge-shaped brooch, Corinium Museum 2012/55/2. Scale in centimeters. No exact find spot has been disclosed for the object, but it has allegedly been found near to a river, most likely not in the water but in the river bank. It comes from Eastington, near Northleach, Gloucestershire. The brooch has been accessioned by Corinium Museum under museum number 2012/55/2. 3 Analysis of an Anglo-Saxon lozenge-shaped brooch 2. Scope of Work The following stages of work were agreed to be carried out: 1. X-radiograph of front and side view of the brooch to illustrate the attachment of the spring to the plate and gain a clear view of the details of the decoration. 2. X-ray fluorescence (XRF)-analysis to establish whether different materials have been used to make the spring, the plate and the materials covering the back as well as the grooves, which visually appear to alternate between grooves and overlie the very thin gilding. 3. Examine the method of gilding (leaf gilding, fire gilding, gold plating or, less likely, diffusion bonding?). 4. Examine whether a solder had been used to attach the (?repaired) spring additional to the apparently two rivets, and if so, what composition it has (XRF). The results of these stages of work are presented in the section 3. 3. Method The XRF analyses have been made at Fort Cumberland, Portsmouth, using an EDAX Eagle II XRF system fitted with a rhodium X-ray tube. Analytical conditions were a tube voltage of 40kV, a current of 1mA, an air path for the X-rays during the analysis of the plate, pin and gilding, and a vacuum for the black and brown materials/?pastes. The X-radiography was carried out by Wiltshire Conservation Service, Chippenham. 4. Results It was possible to clarify completely questions 1, 3 and 4, while for question 2 the queries pertaining to the materials covering the grooves and back of the brooch plate could only exclude certain assumptions, but it was not possible to achieve a conclusive interpretation of the nature of the composite materials present. As already establish during initial examination, the pin plate had been attached by two rivets (Figure 2), their heads only just visible on the top of the brooch plate where they interrupt the zig-zag pattern along the border. No solder had been used additionally to attach the spring plate. The detail of the decoration has been revealed clearly in the xradiograph (Figure 3). 4 Analysis of an Anglo-Saxon lozenge-shaped brooch The XRF spectra for the base materials of the brooch plate and the spring (Figure 5 and Figure 6) are virtually identical and thus indicate that these two elements are likely to have been made out of the same or very similar material, a low tin bronze with small amounts of lead and – interestingly – also traces of silver; the only slight difference in composition is that in the pin spectrum there are two peaks, in front and behind the second Cu-peak, which indicate the presence of Zink. This could not be shown in the area analysed at the back of the brooch plate. Figure 2. X-radiograph showing attachment of pin plate to back of brooch. Exposure: 8 mins at 90 kV Figure 3. X-radiograph showing details of decoration. Exposure: 8 mins at 90 kV The front of the brooch plate was gilded, and the spectrum (Figure 7) clearly shows that the method employed to apply this decoration was fire- or mercury gilding which requires 5 Analysis of an Anglo-Saxon lozenge-shaped brooch the application of an amalgam of gold and mercury with the latter being smoked off by heating the object to about 350°C (Bayley and Butcher, 2004), 42. Some of the grooves on the front of the brooch appeared to be filled with a black material/?paste (Figure 4). It was initially suggested that this material could be niello, a ‘black material composed of one or more metal sulphides which is inlaid or fused into a recess in metal’ (La Niece, 1983), 279. However, the composition of this material did not contain any significant traces of sulphur to suggest it could be a sulphide (Figure 8). Figure 4. Detail of surface decoration on left side of central lozenge with gilding covered by black material/?paste The lack of silver would also be at odds with known compositions of niello in the early medieval period. One recipe for use on gold, given in the Mappae Clavicula, for instance, requires two parts silver and one part copper to at least three parts sulphur (ibid., 281). In order to clarify the nature of this material, further analyses would be required. Analysis of the brown material covering most of the front and back of the brooch has dispelled the hypothesis that it could have been a translucent glass-based (enamel) layer covering both the gilding and black material. The spectrum (Figure 9) is essentially comparable to those of the lozenge plate and the pin; however, the strong iron-peaks indicate that it is essentially a corrosion layer resulting from deposition in an iron-rich environment over a prolonged period of time, commensurate with the alleged find location in a river bank close to water. 5. Catalogue Description Corinium Museum 2012/55/2 Plate Brooch. Complete. Lozenge-shaped plate (W 33.7mm, Th 0.7–1.0mm) ending in thin wire with tip bent into rectangular-sectioned hook functioning as pin rest, now bent out of shape. Plate 6 Analysis of an Anglo-Saxon lozenge-shaped brooch decorated with concentric pattern of seven lozengiform grooves. A wide field (W 4.0–6.3mm) between 6th and 7th groove filled by zigzag pattern of triangles consisting of parallel groves arranged at right angles/acute angles to each other. Antique cut in upper third of right edge of plate. Front surface with remains of fire gilding visible on approximately a third of the area. Most grooves in gilded area containing residues/ are filled with black material/?paste. Rivet heads for attachment of pin plate visible at head tip which is rounded from wear. Subrectangular pin plate with straight end (below plate) damaged, folded up into two lips (indicative of it consisting of two layers), other end extends into spring with 1.5 coils on right side of brooch only; subcircularsectioned pin slightly swollen in middle, tapering to bent tip. Material: Low tin bronze with traces of lead and silver, front fire gilded with additional inlay of black (copper/bronze-based) material in groves. Measurement: L 61.1mm, W 33.7mm, Pin L 57.6mm, Spring Diam. 9.5mm. Figure 5. XRF spectrum of composition of back of lozenge plate 7 Analysis of an Anglo-Saxon lozenge-shaped brooch Figure 6. XRF spectrum of composition of pin Figure 7. XRF spectrum of composition of gilding at front of brooch 8 Analysis of an Anglo-Saxon lozenge-shaped brooch Figure 8. XRF spectrum of composition of black ?paste in grooves at front of brooch Figure 9. XRF spectrum of composition of brown material covering part of front of brooch 9 Analysis of an Anglo-Saxon lozenge-shaped brooch 6. References Bayley, J. and Butcher, S., 2004. Roman brooches in Britain: a technological and typological study based on the Richborough Collection, London, Reports of the Research Committee of the Society of Antiquaries of London 68 La Niece, S., 1983. Niello: an Historical and Technical Survey, The Antiquaries Journal 63(02), 279-97 Additional material, including the raw data and interpretations of the XRF analyses and the x-radiographs are available in the archive. 10