ABOVE: A corrosion potential meter and support equipment, including sampling pipettes, drill and underwater recording slate.

In evaluating archaeological sites we need to know the state of the material now, and how fast is it deteriorating. Ideally we would like to do this without disturbing the site, as this is likely to accelerate decomposition. To develop new techniques it was vital to have a 'test site', where these could be evaluated, and Cellardyke pool provided such a site. The site is discreet, and while survey took a lot of effort, it permitted us to determine accurately locate features relative to each other, and monitor how measured parameters changed with respect to seabed type. Here we could access monitoring equipment at low tide in all but the worst weather.

• Corrosion potentials are an important measurement for modern steel structures, as they instantly inform the inspector whether or not the section of steel is in electrical contact with (and therefore protected by) the sacrificial anodes attached to modern structures to protect them from corrosion. They had also been adapted to some effect to study wreck sites by Ian MacLeod.
• Current transient measurements in principle allow us to take absolute rate information for corrosion processes in situ. Unfortunately these proved too difficult to use outside the laboratory, obliging us to look elsewhere for rate information:
• Control materials are samples of modern materials that are placed on the archaeological site. Changes are measured periodically to give rate information on deterioration processes in that environment. Dave Gregory had developed a 'kebab' system, which tested a wide range of materials simultaneously.
• With test stakes we developed the 'control material' idea in a different direction. We measure the corrosion rate of a number of identical samples of a single standard test material (mild steel to BS). Samples are placed around the site, and allow us to compare one part of the site with another, ot with other sites where similar measurements have been made. The test samples are held in a perspex stake embedded upright in sediment on the site. Measuring changes in height of the top of the stake above the seabed therfore also allows us to monitor small changes in sedimentation patterns at that point.

Link: Explore Cellardyke pool in this 3-dimensional rendition (requires a free VRML plugin for your browser).