The Stirling Castle Wood Recording Project was designed as a trial to compare and evaluate traditional and innovative recording techniques for waterlogged wood. Stirling Castle was a post-medieval ship, built in 1699 and lost during the great storm of 1703 on the Goodwin Sands, off Kent, Great Britain (Ensor 2004). Recovery of the wreck was undertaken in 2006 by Wessex Archaeology, on behalf of English Heritage. A small piece of waterlogged wood from the wreck (most likely a barrel fragment) was provided to researchers at English Heritage and the University of Southampton for analysis and recording. This included traditional recording techniques such as photography, illustration, x-radiography, silicone rubber moulds – as well as innovative recording techniques such as laser scanning and Polynomial Texture Mapping (PTM).
The purpose of the project was to compare the various recording methods using a variety of parameters and criteria, including the amount of skill needed, the accuracy of the output, the ease of using the data, and the time required.
The following techniques were used to record the waterlogged artefact:
- Hand Drawing
- Silicone Mould and Cast
- Laser Scan
The easiest and fastest way to capture the general shape of an object is by sketch. This is commonly done on site when the first record of a timber is created, normally on a wood record sheet. Annotating the sketch gives the added benefit of marking damage, tool marks or dimensions.
A reasonably detailed and accurate record is obtained when creating a hand drawing at scale 1:1. This is commonly done before any conservation treatment is attempted to keep a record of the pre-conservation dimensions. A hand drawing also allows putting emphasis on details that are difficult to illustrate with a photograph.
An accurate depiction of a timber can be achieved with an illustration at scale 1:1. Drawing of timbers before conservation is a common method to record dimensions and the position of natural features (eg. grain), working marks (eg. tool marks, constructional features) and areas of damage (eg. abrasion, wood borer damage).
A quick record of a timber can be obtained by a photograph. Digital photography is now widely available and commonly used. Fine surface details are difficult to capture on wet, dark timbers and good lighting and some experience and patience are necessary.
This visualisation technique is not commonly used for organic materials, although it is becoming more recognised (O’Connor and Brooks 1007). When Earwood notes that some constructional details such as dowels can only be observed if wooden vessels are being dismantled (2993, 175), no consideration was given to non-destructive investigative techniques such as x-radiography. In this study x-radiography was used to examine one of the wooden dowels inside the head piece.
This well established technique accurately captures surface features and allows for close examination without needing the object or for reproduction in form of casts. The silicone rubber mould captures shape, size and direction of surface features in a reversed “negative” way. A “positive” can be obtained by casting a replica using plaster of Paris or resins. Surface details on the mould or on the cast can be viewed without any aid or examined closely under the microscope or Scanning Electron Microscope without having to handle the original artifact. Often photography is used in combination with this technique which is ideally suited for a comparison of tool marks on different artefacts.
Laser scanning or non-contact digitising is becoming an increasingly common tool for conservation recording and analysis. The value of such techniques for cultural heritage visualization was recognised almost as soon as the technology was developed. All instrument settings were set to the highest possible capture quality for this study.
Polynomial Texture Mapping (PTM) was invented by Hewlett Packard Labs in 2000 (Malbender et al 2000). This technique employs a fixed position digital SLR camera and records multiple frames with varying light source directions. These frames are then compiled into a 3D model that enables interactive movement of a ‘virtual’ light across the object—thus allowing researchers to detect surface details otherwise difficult to detect and study.
Surface comparison of pre and post-conservation wood
The project also evaluated the quality of surface detail evident in pre and post-conservation wood. To determine this, the barrel fragment from the Stirling Castle was recorded (using high-accuracy techniques such as silicone rubber moulds, laser scanning, and Polynomial Texture Mapping) before and after conservation. The data was then compared, revealing significant changes in the wood’s surface detail through the treatment process, thus highlighting the benefits of recording waterlogged wood prior to conservation.
The published paper is available on the English Heritage website
- Angela Karsten (English Heritage)
- Graeme Earl