NCPTT-Funded Research at Prominent Galleries Will Aid Conservation of Gilded Objects
A PTT Grant administered by the Center in 2001 continues to yield useful results in the study of gilded objects at the Smithsonian’s Freer Gallery of Art in Washington D.C.
The study involves the use of “eddy currents”—essentially, pulsed currents of electricity emmited from a hand-held probe. The electrical current has been traditionally used on metal to detect flaws, corrosion and other anomalies, much like archeologists use ground penetrating radar to discover buried objects. In this study, however, the project team used eddy currents to measure the thickness of gilding on a museum piece.
According to Blythe McCarthy, project leader, the study evolved from the Gallery’s hope to discover non-destructive testing methods for artifacts.
“Originally, we wanted to determine whether tin layers were present on the surface of bronze weapons in Freer’s museum collection,” McCarthy said. “When we identified eddy current techniques as a possibility, we decided to first apply it to the slightly simpler problem of gold on bronze.”
As the method is perfected and adopted, it could replace the common invasive practice of removing cross-sectional samples for analysis.
The yearlong project involved setting up an eddy current test system, manufacturing reference test samples and then testing the samples. Using those results, the test methods were applied to actual museum objects.
Test measurements were able to discern differences between gilding layers of varying thickness, and also between gilding layers of varying composition. Measurements made on the Freer Gallery objects were consistent with reference sample results for mercury amalgam gilding.
McCarthy says the findings hold potential significance.
“We are excited by the results we have found so far and plan to continue research in several areas,” she said. “Our initial work with pulsed eddy current techniques appeared promising and we will pursue this further.”
The team also plans to further study the effects of differences in gilding composition and thickness on the eddy current measurements in order to better understand the effect of corrosion products on the measurements, expand the use of eddy currents to the study of other metals and to develop a more user-friendly system.
The eddy current project is one example of NCPTT’s goal of emphasizing preservation technology research. According to McCarthy, the effort also made possible a wider cooperative effort.
“The support NCPTT provided was invaluable in enabling the collaboration between the Freer and Sackler Galleries and Johns Hopkins University,” she said. “In addition, the purchase of materials for the standard samples, as well as specialized probes for the eddy current measurements would not have been possible without NCPTT funding.”
While research continues on the use of eddy currents for the measurement of gilding layers, researchers involved with the project are optimistic that the methods they are studying will become a commonly-accepted weapon in the arsenal of non-invasive techniques available to conservators and scientists for studying art.