AIC's 52nd Annual Meeting

Egyptian limestone objects are known to be sensitive to unstable conditions in storage. Exposure to fluctuating humidity can cause the soluble salts inherent in these objects to dissolve, migrate, and recrystallize leading to delamination, flaking, and general loss of structural stability. The Walters Art Museum found three such objects in their collection in need of stabilization through desalination. These Egyptian limestone works were determined to be too fragile to be treated through the traditional desalination approach of submersion in a water bath. The conservators sought an alternative approach to desalination with agarose hydrogel poultice, which desalinates the stone through the formation of a concentration gradient. Prior to treatment, the surface will be secured with B-72 consolidant to preserve its structural integrity.

This research explores the effect of consolidation on the rate of desalination and the efficacy of the treatment using an NMR-MOUSE spectrometer, a non-invasive analytical technique that measures the transverse relaxation time (T2) of the protons in limestone-bound water. As such, T2* rates measured over the course of the treatment allows direct observation of the salt changes in the stone. Preliminary data suggests that the non-consolidated stone reached full desalination after 5 days compared to the consolidated stone which took 11 days. The data suggests that use of an agarose hydrogel treatment is feasible even after the application of the B-72 consolidant.

In addition to NMR relaxometry measurements, ICP-MS, SEM-EDX, and a series of microchemical tests were employed to analyze the salt composition of powder which had delaminated from the three Egyptian limestone objects found in the Walters Art Museum’s collection. Quantitative evidence of Na+, K+, and Mg2+ cations were found in each sample in addition to the likely presence of phosphates, sulfates, and chlorides. This project advances the understanding of the use of agarose hydrogel for the desalination efforts of fragile objects. The NMR-MOUSE and other laboratory instruments can be applied to the cultural heritage field to better understand the treatment approaches already in use and to assist the development of new processes. This collaborative effort between the scientific research and art conservation fields exemplifies the knowledge that can be gained through interdisciplinary work.

This research was performed as part of the Baltimore SCIART Program, which is supported by the Andrew W. Mellon Foundation under Award 41500634.