News from the Conservation Lab — Exploring bronze corrosion under the microscope – The Kelsey Blog

News from the Conservation Lab — Exploring bronze corrosion under the microscope

Harrison Biggs at the microscope.

This month we’re excited to welcome Harrison Biggs as our Conservation guest-blogger! Harrison is interning in the Conservation lab as part of the Museum Studies Undergraduate Program.

By Harrison Biggs, Conservation Intern

This semester I’ve been given the opportunity to work with Carrie and Suzanne as an intern here in the Kelsey Conservation lab. As an intern, I’ve been doing a lot of multispectral imaging and XRF analysis for the ongoing NEH Color Research project, but the project I’ve been most excited about lately is the treatment of this little bronze statuette (KM 3090).

Bronze Isis and Eros figurine. Graeco-Roman Egypt. Purchased from David Askren, 1925. KM 3090.

Even though treatment in this case just means picking harmful materials off the object with a pin (it’s more fun than it sounds), this has been a great opportunity to learn about the ways that bronze objects age. Bronze corrosion is an incredibly complex process where even small environmental changes can lead to the generation of drastically different minerals and patterns, but there are a few minerals that appear more than others.

Cuprite (Cu2O), a red-orange-brown copper oxide, and Malachite (CuCO3-Cu(OH)2), a pale green copper carbonate, are fairly common corrosion products that often form protective patinas on ancient bronze objects. Azurite (2 CuCO3-Cu(OH)2) is a less stable copper carbonate that tends to manifest as small blue crystals on an object’s surface. Nantokite (CuCl) is a soft, waxy copper chloride that forms commonly under burial conditions. When it gets too moist, Nantokite transforms into powdery, light green Paratacamite (Cu2(OH)3Cl), commonly referred to as “bronze disease.” Paratacamite is the main target of the treatment because, if allowed to spread, it can reduce an object to powder.

Together with a pile of less common and similarly colored minerals, these form a beautiful little world that I have the privilege of staring at through a microscope for hours at a time. I hope you enjoy looking at it as much as I do!

The surface of the figurine under 10x magnification.

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