The virtually uninvestigated composition of bronze alloys in 17th-century Rome is a key data point for our study. We use two techniques for these analyses.

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1. X-Ray Fluorescence (XRF): a portable and non-destructive technique, provides data on the composition of the bronzes. The AGO has purchased a Bruker 5G Tracer that has been calibrated for use by the project. The AGO Bruker travels with the team and is operated by one of two NRCAN licensed operators (Rizzuto, and Ellis).

2. Inductively coupled plasma-tandem mass spectrometry (ICP-MS-MS): We also remove small samples of metal from the bottom or back of the sculptures for ICP-MS analysis of trace elements in the alloys. With a detection limit of 0.1 to 10 parts per billion for 69 different chemical elements, this sensitive technique allows us to trace the re-use of metals and to better understand the sources of copper in 17th-c. Rome.

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What the data can tell us:

1. Sources of bronze: From documents we know the sources of reused metals for some projects (e.g., Lamouche 2013c, Rice 2008). It stands to reason that identified objects made from these sources will have comparable trace elements (which do not change with re-use).

2. Alloys and Foundries: a database of the alloys of Bernini’s bronzes may enable us to link works to each other, tie them to specific foundries, show recipes for alloys used for specific object types, and determine if primary-source or contemporary alloy recipes are reliable sources of data.

3. Alloys and Gilding: Alloy data may determine if specific alloys were chosen for the many bronzes that were gilded, testing Bernini’s recorded comment about ideal alloys for gilding (Chantelou, MacLennan et al, D’Amelio).
 

Initial results: Some preliminary results show alloys clustering by typology (e.g., portraits, medallions). Samples hand couriered to Bourgarit’s lab await characterization.