College Honors Program

The Creation and Removal of Iron and Manganese Oxides on Terracotta Surfaces

Date of Creation

5-31-2023

Document Type

Campus Access Only

First Advisor

Ellen E. Perry

Abstract

A 5th-century BCE Greek red-figure terracotta pelike of Paris and Helen at the Harvard Art Museums has a stain consisting of manganese and iron oxides. While previous studies have examined metal stains on nonporous surfaces, less is known regarding their removal on porous surfaces, like terracotta. The goal of this project is to investigate the safe treatment and removal of manganese and iron stains on terracotta surfaces. First, manganese and iron salt solutions, in series with sodium hydroxide, were brushed onto the surface to develop stains that adhered to the terracotta surface. To confirm that the stains adhered, XRF was used to analyze the elemental composition of the sherds. 3 poultices, soft materials, were soaked in 3 chelator solutions, EDTA, DTPA, and HBED, in order to determine the best method of removal of the stain. A chelator can chemically bind to the metal, with the purpose of removing the metal from the surface of the terracotta. After the removal, SEM data was collected to determine the effectiveness of the chelator and assess which metals were removed.

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