Conservation

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Conservation

Introduction

The aims of the conservation work undertaken on the artefacts were to ensure their preservation, and to reveal, analyse and record information relevant to the manufacture and use of these objects. For a general introduction to archaeological conservation see 'The Team', 'The Conservator' in Mainman 2001.

Methodology

Conservation followed the phases of involvement, as identified by English Heritage 1991: phase 2 fieldwork, phase 3 assessment of potential for analysis, phase 4 analysis and report preparation, and phase 5 dissemination.

Fieldwork

Radiography of the artefacts was carried out according to usual YAT procedures (see O’Connor in AY 17/06 p.468). From the radiographs it was possible to identify material type, object shape, and in some cases associated features obscured by corrosion, as well as the structural condition of objects. Slag and metalworking debris were positively identified and non-ferrous surface coatings were detected. Radiography also assisted the numismatist in identifying a number of coins.

Assessment of potential for analysis

At this stage the condition, stability and packaging of the finds were assessed and urgent first-aid treatments (such as stabilisation and consolidation of wet-packed finds) undertaken. Four percent of the finds underwent some form of conservation treatment. Indicators of unusual conditions of preservation were noted, and the potential for further analysis and research was discussed. Recommendations for investigative conservation, for additional specialist support and further research were suggested. Sampling strategies were applied, as the large number objects (1410 small finds) meant that full assessment on every object was impractical within the available resources (see Jones et al. unpublished; Jones unpublished; Vere-Stevens unpublished.

Analysis and report preparation

Six percent of the assessed finds were selected for further investigative conservation in liaison with finds researchers, guided by recommendations in the assessment reports. Treatment was carried out according to YAT procedures (see Buckingham in AY 17/09 pp.1218–1221, Spriggs in AY 17/14 pp.2467–70, Spriggs in AY 17/13 pp.2095–2100 and leather AY 17/16). Treatment details vary and are recorded in the Conservation work record for each artefact (click on the SF number to see these records). Conventional mechanical methods were used to remove external soil and corrosion. The silver, copper alloy, lead and bone finds were fragile so softer glass bead powder or compressed air on its own was used successfully for cleaning.

Metalworking debris, coins, wood preserved in iron corrosion, and selected stone, shale, antler and bone artefacts were referred to appropriate specialists for identification. X-Ray Fluorescence (‘XRF’) analysis was carried out on selected finds using a Links System XR200 EDXRF spectrometer. The equipment was operated at 50KeV at 350mA with a copper filter and no vacuum.

Dissemination

In order to make the information held in the X-ray archive accessible for publication on the web, the original radiographic plates were digitised at 512 dpi at Bradford University using a Howtec medical scanner (O'Connor and Maher 2001). Two CDs were produced, holding high-quality images of each plate. Where the image of an object extends to within a few millimetres of the edge of the plate it was masked by the template during this process; for some objects researchers may need to refer to the original plate. The large TIF files provide maximum information for researchers, but are very slow to load. These large files were reduced in size, enhanced, labelled, and linked to each find record, often providing the only image of an artefact on the database. In some cases the image of an individual item was selected from the plate and manipulated to reveal more detail (SF00866).

Results

This section details the information revealed during the conservation, covering only the artefacts from the York Archaeological Trust excavation (context 1200 onwards); it does not include finds from the 1999 Time Team excavations.

Metals and metalworking debris

Iron
A total of 22 iron objects were investigated and revealed a wealth of information. An iron key with copper alloy chain, SF00865, revealed a circular key bow with a solid stem and a ward cut in the inner and outer sides, possibly attached to the chain with nineteen links, each link with looped ends. Fragments of an iron object SF00806 were found together on site, and investigative conservation allowed reconstruction of a perforated strap fitting with a large loop at one end. A wide variety of craft tools were identified: e.g. a sickle SF00737, a fibre processing spike SF01210, a knife tang SF01287, a spike or punch SF01288, a possible punch SF01312, a needle SF01363, and the possible stem (incomplete) of a barrel padlock key SF01440. Several other objects SF00965, SF01005, SF01068, unidentifiable before conservation, were identified during and after conservation as knife blades and knife tang fragments.

In the assessment four iron finds were selected for species identification of the mineral replaced wood evident on parts of the objects. The YAT wood technologist, following Schweingruber 1982, identified the wood species. One find SF00931 was found with Quercus sp. (oak) remains, the piece having been driven into the tangential longitudinal surface of the wood. One knife tang SF01287 had Fraxinus excelsior L. (ash) remains. The other two finds, SF01068 and SF01287, had mineralised remains of close-grained hardwoods.

In some cases the corrosion products also contained material from the surrounding context, such as charcoal, and both flake and spherical hammerscale, suggesting proximity to a metalworking area. Hammerscale was also noted during investigative work on SF00737, SF00806, SF00965, SF01005. A powdery red haematite-like corrosion was observed on one find, SF01317, which could indicate a high temperature activity (Cronyn 1990 p.180). In some cases the corrosion incorporated mineralised plant remains in various orientations, suggesting they were not part of the object.

Copper alloy
Twenty-eight small finds were treated. The decorative features of a complete binding strip were revealed: moulded animal heads with prominent eyes and ears and zig-zag ornamentation (SF01265). A D-shaped buckle was decorated with a central projection SF00701, and an annular brooch SF00999 was decorated with triangular shapes. Square and rectangular forms decorated a book clasp SF01038. Structural features were exposed, including a D-shaped buckle and pin SF00546 and a possible terminal piece SF01470 with sphere, leaf forms and areas of gold-coloured surface. The cross-section of SF00588 confirmed this as a needle rather than a balance fragment. Localised investigative work revealed an unusual deposit that might be the remains of a filler or coating on a possible mount (SF01187) and fragments of an unusual black deposit (possibly mineralised leather remains) sandwiched between the rectangular plates of a strap-end (SF01264). Tool marks were often revealed, for instance on SF01500, SF01548 and SF01556. It was observed that one strap-end SF01500 had remains of possible white metal solder, which was confirmed by XRF analysis (see below).

A quantity of scrap metal, slag and ‘spillages’ was noted during the assessment stage, and some details found during further investigation might also be evidence of metalworking or re-use on the site (e.g. SF00785). Slag-like material was found within corrosion crusts in the form of tiny spheroidal hammerscale (SF01410 and SF01411).

Lead
From the 23 lead finds that were assessed two were selected for further conservation treatment. The conservation work exposed linear impressions, tool marks and a countersunk perforation on a possible weight SF01002, and cast interlace decoration on a possible mount SF01144.

X-ray of SF01144

Mount before treatment

Mount after treatment

Silver
All four of the silver finds were selected for further conservation. Three were coins, which are discussed below. The remaining find, SF00784, is a possible mount, and treatment revealed constructional details such as an irregular punched central hole.

Coins
Five of the thirteen coins recovered could not be identified by the numismatist at assessment stage. Following localised corrosion removal all five have been positively identified as medieval. Two were copper alloy (SF00866 and SF01303) and three silver (SF00949, SF01304, SF01521). One coin, SF01521, was identified as having a York mint mark.

X-ray of SF01521

SF01521 obverse after treatment

SF01521 reverse after treatment

X-ray fluorescence spectroscopy (XRF)
This technique was used to investigate qualitatively the elemental composition of selected surfaces. As a result it has been possible to classify some of the material. Evidence of non-ferrous plating revealed during investigation was confirmed. XRF analysis confirmed a tin plating on a buckle SF01240, a dress pin SF01588 and an iron fragment SF01299. A tin-rich solder was found on a strap-end SF01500. A mount SF00784 was confirmed as being silver. Four crucible fragments produced a spectrum which was consistent with copper production (SF01098, SF01671, SF01672, SF01685).

Inorganic (non-metallic) material

One glass bead SF01509 required further cleaning prior to illustration and photography. One plaster fragment SF01087 required consolidation treatment to provide structural stability and enable handling and study. Four mould fragments (SF00815, SF01431, SF01442, SF01681) required further cleaning for illustration.

Organic material

Leather
Eight leather artefacts (SF00618, SF00619, SF01052, SF01542, SF01543, SF01544, SF01598, SF01599) were recommended for detailed recording and further treatment. The objective was to stabilise the leather for long-term storage and future research. For a detailed description of the leather finds see Jones et al. unpublished, and Vere-Stevens unpublished.

Bone and Antler
The majority of the artefacts of these materials were conserved at the initial assessment phase in order to stabilise them. During the analysis phase, four horn core fragments (SF01193, SF01365, SF01505, SF01513) and one antler tine SF01508 were cleaned for photography. The saw marks evident on the antler tine at the time of assessment were defined. A spindle whorl SF01330 was also reconstructed.

Jet
One jet bead SF00769 was consolidated to stabilise the structure.

Discussion

The majority of the excavated small finds consisted of inorganic materials: iron and copper alloy, slag and fired clay. With the exception of the lead material the metal objects were heavily corroded, and exhibited bulky corrosion products which are commonly found on objects from moist, aerated contexts. The poor condition of the metals may have also been influenced by industrial activity on the site, providing an aggressive and corrosive environment.

These conditions are not ideal for the preservation of organic objects such as wood and leather; no wooden small finds were retrieved. The bone and antler artefacts from the site were all in a good condition; this is normal owing to the survival of their inorganic component. The vulnerable organic finds however, such as leather, were fewer in number and were in poor condition. Some structural timbers (see Structural Timbers report) were retrieved and vivianite was noted on one metal item SF01231 indicating possible waterlogged phosphate-rich layers within or near its immediate context. There is, therefore, considerable potential for survival of organic materials below the levels excavated.

Only one new conservation treatment was used, namely air abrasion using glass bead powder, which revealed surface details on coins and tool marks on a lead alloy artefact. The glass bead powder abrasion was very effective as a gentle cleaning method and is recommended for treatment of fragile surface layers on copper alloy or lead objects.

The introduction of Information Technology has provided the most radical change to our practices: computerised conservation records, the use of digital cameras to record work as it progressed and scanning of images into the database has enhanced the information recorded in the site archive, made that archive more secure and facilitated communication with colleagues and specialists.

Conclusions

Detailed investigation of many of the objects was undertaken, revealing a wealth of information that would otherwise not have been recovered. Obscured by dirt and corrosion, technological details such as tool marks, hammered ends, joining methods, surface coating and decoration would possibly have gone unnoticed. Despite the poor condition of the metals, the detail revealed by localised corrosion removal was much greater than expected.

The conservation contribution to this project was designed to maximise the information potential from the artefact assemblage, in a structured and methodical manner. The results of this work have provided the artefact researcher with well-documented, well-packaged, clean and stable objects for study, illustration and archiving.