Quantitative Assessment of Impact and Sensitivity of Imaging Spectroscopy for Monitoring of Ageing of Archival Documents

Abstract

Ageing of historical documents often results in changes in the optical properties of the constituent materials. Imaging spectroscopy (IS) can be a valuable tool for monitoring of such changes, if the method fulfils two important conditions. Firstly, compared to natural ageing, the accumulated light dose from repeated measurements of the monitored document must not induce any significant degradation. Secondly, the monitoring instrumentation and procedures should be sensitive enough to detect changes in the materials before they become visible. We present experimental methods to evaluate the suitability of IS instrumentation for monitoring purposes. In the first set of experiments, the impact of repeated monitoring measurements was determined using a set of Blue Wool Standard materials. In the second set of experiments, the capability of the instrument to detect spectral changes was tested using ISO standard materials and several documents representative of European archive collections. It is concluded that the tested hyperspectral instrument is suitable for monitoring of the colour change of documents during display. The described experimental approach can be recommended to test the suitability of other imaging spectroscopy instruments for monitoring applications.