and contractors employed for investigation works should be selected with the same sensitivity as for conservation repairs. It is important to recognise where metal tongued or secret nailed boards cannot be lifted and relayed without damage, and where alternative investigation techniques may be less destructive. Fibre-optic borescopes provide an invaluable means of inspecting concealed voids. Several versions are available for building surveys providing a range of light power, po1tability and flexibility. In principal, light from a powerful bulb is transmitted via a bundle of optic fibres to a scope with precision optical lenses. The principal choices of equipment are between rigid or flexible borescopes ORION HERITAGE MANAGEMENT SYSTEM • Listed Buildings • Property Management • Museums and general Heritage use Linked if reqnired to digitised imai:es (e.g.35mm slides or photographs), plans and maps • Windows based • Single or multi-nser • Works with mid-range PCs • Flexible and user-friendly • Allowing fast access and resolution of queries • Complying with latest EU Recommendation • Built-in comprehensive Help fdes • Scanning and data conversion services Clients include major heritage organisations Comprehensive leaflet from: ORION IMAGING LIMITED Tel 01633-868811 Fax:01633-868968 E-Mail: orion@dial.pipex.com Whether it is a bespoke lantern for the Metropolitan Police or restoration of a lantern for St.Paul's Cathedral, the craft and technical expertise of D.W. Windsor Limited will stand and deliver the goods. I SPECIAL PROJECTS DMSION == Tel: (01920) 466499 • D.W. Windsor Limited, MarshLane,Ware, Herts SG12 9QL C:I 14 Magnified dust shavings: top Anthrenus (ca1pet beetle) larval skin; middle Anobium punctatum (woodworm) and Lepsima Saccharina frass pellets; bottom Xestobium ruforillosum (death watch beetle) frass. and battery or mains power. In practice the difficulty of maintaining a sense of orientation through a flexible scope complicates the interpretation of any observations. The penalty for the most brilliant mains-powered light intensity is a relatively large cumbersome unit. However, this is preferred to the undoubtedly more portable battery equipment because their convenience comes at the expense oflight quality and it can be rather difficult to distinguish between cobwebs and fungal growth in the weaker yellowish hue produced. A small access hole is required, approximately 12 mm diameter. Where available it may be possible to utilise existing holes (old service pipe holes or damage board edges). New inspection holes may be discreetly sited and either plugged after use or retained for future routine inspection. In practice, even with the most powerful instrument, the field of view is deceptively short and the range of vision tends to be no more than 1 m. Inspection holes are therefore located where they are expected to reveal the most information, in suspected areas of worst decay, or to achieve the clearest view of the structure. Whilst it may not be possible to view all details clearly, it is usually possible to see sufficient clues to determine whether or not decay is suspected, and would necessitate further investigation. Identification of concealed decay is particularly a problem behind valuable wall panelling, and dust analysis can provide many clues to detect the presence of bio-deterioration. Samples of accumulated dust and debris dislodged from panels and their fixing timbers are collected from beneath the skirtings. The sampled material will typically comprise NEWTECHNOLOGY FORCONSERVATION ® ® High-powered fibre-optics in use through existing gaps to investigate behind oak wall panelling. dust, sand, mortar and plaster granules. The presence of decayed wood or insect fragments and distinctive •bun-shaped death watch beetle frass can be detected by examination with the naked eye. Magnification using a hand lens (X 10) is necessary to distinguish the smaller lemon shaped frass produced by woodworm. More powerful microscopic examination is used to identify other domestic insect pests which may be attacking other organic materials and may indicate associated environmental problems. SURFACEOR SERIOUS Substantially sound timber is often unnecessarily discarded because its surface was decayed when probed with a trusty penknife. However, the sapwood of timber is generally rather susceptible to decay and beneath the superficial outer damage its greater proportion of more durable heartwood often remains sound and structurally adequate. Tapping the timber to detect decay may also be misleading as the hollow sound produced by concealed decay may not be distinguished from loosely fixed timber. Until recently the usual method of checking such an initial diagnosis would be to drill with a standard auger bit and to judge whether the timber felt sound, soft, or decayed. The Sibert decaydetecting drill is a comparatively recent innovation which supersedes this subjective testing. (This was the subject of an article in Context 39, September 1993,p.25).Thereareinfiniteapplications including testing the integrity of beam bearings, detecting concealed decay in plates where only one face is accessible, checking the condition of mortice/tenon joints and assessing the depth of firedamage charring. It is possible to test CONTEXT49
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