Climate-Induced Change Pilot Study

This pilot study emerged from a 2015 experts meeting, which explored the possibilities of adapting an epidemiological approach to cultural heritage. The study monitors the condition of a small collection of wooden objects under controlled humidity variations. The pilot tests and develops a small toolkit of techniques for quantifying damage that may be used in a larger series of prospective cross-sectional studies.

The goals of the study are:

Establish reliability and reproducibility of different methods in recording condition changes and whether there is correlation between scientifically accurate measurements (e.g., acoustic emission) and observational techniques

Establish relationship between micro-damage development and climatic conditions for susceptible wooden object(s)

Obtain a quantitative assessment of variety and range of mechanical damages that occur in the pilot study collection that can be attributed to climate fluctuations (clarify environmental responses)

Contribute to establishing a framework or guidelines that could be applied by other institutions or individuals that assesses the correlation, causality, credibility, and uncertainty of climate induced change/damage in objects

Explore evidence base for the concept of climatic "proofing" in objects

The pilot study, undertaken in a climate-controlled space, involves a number of wooden objects, offering a variety of types of wood, thicknesses, and different kinds of construction and finishes. These historical objects, which have some climate-induced damage such as cracks and warping, are not museum objects. They were acquired for the study, either through purchase or through loan. In addition to the historical objects, a white oak cleated panel, made by the J. Paul Getty Museum Preparations Department for this study, was included to represent an object with no prior climatic proofing. Damage caused by the experiment to any of these objects is anticipated and acceptable.

Temperature in the space is kept constant at 72°F (21°C) and the relative humidity (RH) is held at different levels for set periods of time to allow for the objects to fully respond to the conditions. Based on the materials and their thickness, RH is held at a stable level for a minimum of 4 weeks to achieve equilibrium.

The RH scheme focuses on behavior at low humidities, since these are expected to result in the most recordable damage, which will help align the monitoring methods. One excursion to higher RH (65%) at the beginning of the pilot study is undertaken to increase the moisture content of the wood, inducing some compression stresses (especially in the newly constructed white oak panel), which could contribute to potentially higher shrinkage stresses at lower humidity. Even though the excursions of RH exceed current recommended museum levels, the conditions are not unlike what objects could experience in an uncontrolled environment, for example in a historic house in Southern California.

Monitoring Techniques

A variety of monitoring techniques are deployed to record how the objects adapt to the climatic changes they are exposed to. These methods are also assessed for their reliability and reproducibility in recording condition changes and whether or not there is some correlation between scientifically accurate measurements (e.g., acoustic emission) and observational techniques.

The study combines the application of acoustic emissions (AE) monitoring with physical measurements and photographic documentation. The data obtained by this suite of documentation techniques of varying sensitivity will be compared.

While this controlled exposure experiment remains in progress, preliminary results show that moderate fluctuations of RH did not result in the development of new fractures or crack propagation for the wooden objects studied during this experiment. The influence of increasingly larger RH fluctuations will be further analyzed.

The study will result in:

Analysis of the data (AE, dimensions, images, error margins) and evaluation of the correlation between the different monitoring methods

Establishing climate-induced damage functions (strain modeling) to further investigate broader environmental conditions

Page updated: August 2017