Tone M.Olstad and Annika Haugen
The installation of heating systems in the unheated churches in Norway in the first part of the 20th century was, after a period, thought to be the cause of damage to the polychrome wooden objects in the churches. From the end of the 1970s, localised heating in churches has been seen as a way to minimise the climatic impact on the wooden objects. There were however in the 1990s still a number of unanswered questions concerning the climatic stress put on the painted wooden objects. In the research project Ecclesiastical Art – Climate and Dimensional Changes led by The Norwegian Institute for Cultural Heritage Research, the dimensional changes in the surface of the wood were registered. Two of the results from the project were of special interest: the surface of the wood reacted extremely fast, just a few minutes after a change in the environment. In addition it appeared that relatively larger dimensional changes occurred over distances of one millimetre than in distances around 100 millimetres. A change in the environment seemed to cause both swelling and shrinking in the micro distances while the larger distances seemed to be dominated by either shrinking or swelling. NIKU is in 2007 starting a cooperation with the Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, in a project with the aim of finding a method of observing reactions in painted wood when exposed to a varying climate. Documentation of changes in the paint layer by laser vibrometry and direct monitoring using acoustic emission will be tried out, complemented by computer modelling. In 2007, Gotland University and NIKU start a project trying to find out whether intermittent heating really has damaged polychrome wooden objects in the churches. Between one and two hundred objects, placed both in heated, unheated and intermittently heated buildings, are planned to be investigated. Hopefully the two projects will create a basis for defining whether the intermittent heating is damaging the polychrome wooden objects in our churches.