Dowels, powder and cracks: Collaboration in the preservation of a 12th-century portal from Bordeaux

Barbara Mangum and Valentine Talland

Abstract

For several years the Gardner Museum has been monitoring some cracks in a large late 12th century Portal from Bordeaux made of a calcareous feldspathic sandstone and set permanently into a gallery wall. It was first proposed that the cracks may be related to corroded metal pins holding the Portal in place. A private X-radiography company was called in to take X-rays in situ of the areas which might contain metal pins. Robert Baboian, corrosion engineer and consultant on the restoration of the Statue of Liberty, joined the museum’s conservators in evaluating the X-rays and in discussing the possibility of corrosion-related damage. Further examination of the cracks in the stone and study of the architectural history of the wall into which the Portal is set raised questions about structurally-induced stress on the Portal. With support from the National Endowment for the Arts, the structural engineering firm of LeMessurier was consulted to analyze the building materials of the floor above the Portal and ultimately to set strain gauges across the cracks to measure stress on the Portal in relation to visitor traffic on the floor above. The study was conducted during the museum’s Christmas event during which time some 350 visitors pass to attend a concert in the gallery directly above the Bordeaux Portal. The analysis indicated that visitor use in the gallery above did induce measurable strain in the cracks of the Bordeaux Portal. This project has been a great opportunity to bring in technologies not routinely applied to art conservation as a method for expanding our understanding of the condition of an artifact.

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