AIC's 47th Annual Meeting

Reducing the energy intensity of museums, galleries and other spaces with heritage collections is increasingly important due to the high cost of fuel, and the global need to lower greenhouse gas emissions. At the front line, institutions are seeking to lower energy consumption by addressing inefficiencies related to building design, HVAC and lighting equipment, and environmental control strategies. In a parallel effort, researchers are rethinking the necessity of precise museum environment tolerances, by investigating the risk of damage to specific materials exposed to fluctuating relative humidity (RH) and temperature. The goal of this latter body of work is to define the conditions that achieve an acceptable balance between facility energy consumption and the risk of collection damage. As a contribution to this effort, a research project is currently underway at the Canadian Conservation Institute that uses acoustic emission (AE) testing to monitor, or ‘listen’, to model wooden structures during exposure to humidity extremes. Under conditions causing physical damage, acoustic signals are emitted by the test materials, which are subsequently detected and analysed through the AE instrumentation. One of the many challenges with optimising the museum environment is the dependence of humidity sensitivity on exposure history. It is reasonable to assume that sensitive objects exposed to RH extremes have experienced past damage, and similar repeated fluctuations will have little or no harm. This is known as the Kaiser effect in AE terminology, or the concept of ‘proofed fluctuations’ in the field of heritage conservation. There are, however, foreseeable exposure histories where the Kaiser effect may fail or, at least, require further attention. For example, the resetting of hide glue in wooden assemblies at high RH may lead to further damage at a repeated low RH cycle. In order to study the effects of both humidity magnitude and history, a custom environmental chamber was constructed to generate fluctuations through various control modes: square wave, sinusoidal, custom array, and cloning of an external environment through cellular communication. Samples exposed to prescribed RH conditions in this low-noise test chamber were monitored with a multi-channel AE system to detect damage. This talk will provide an overview of research work to date, with a focus on the apparatus design and ongoing experiments. Preliminary test results highlight the response of simple wooden joints and veneered assemblies, which were bonded with animal glue and exposed to cycling humidity. The findings complement other research involving AE as an early warning monitoring tool for collection damage.