12th century copper alloy bowl with figurative decoration, private client
This bowl was found by a metal detectorist at a site in Kelshall, Hertfordshire. Despite being in very poor condition, with extreme thinning, deformation, fracturing, corrosion and loss of the metal due to the burial environment, treatment did improve stability, as well as make the remarkable incised decoration on the interior more visible.
Before any treatment could be undertaken, ‘papier mache’ supports (acid-free tissue and wheatstarch paste) conforming to both the interior and exterior surfaces were made. These enabled the bowl to be fully-supported during treatment, also aiding handling and turning of the fragile object as it was worked on.
Treatment began by cleaning the surfaces using mechanical methods (swab stick, scalpel) under magnification to remove remains of burial dirt. Where possible and appropriate, this was followed by reduction of corrosion layer/s, again using a scalpel under a microscope. Localised spot treatment of apparently unstable corrosion was undertaken to convert these areas to more stable compounds.
The corrosion layers were extremely thin but unfortunately had affected the original surface in multiple locations. Corrosion removal was therefore limited to areas where a stable, intact layer remained beneath, but did aid in revealing intricate incised figurative decoration on the interior of the bowl. The nature of the decoration, including trees and robed figures with haloes holding large bound books (as seen in one of the images below), is suggestive of Christian iconography.
Fractures and loose elements were stabilised and supported using Japanese tissue ‘sutures’ and an acrylic resin, whilst losses in severely weakend areas were minimally filled using light, inert filler with an acrylic resin, all toned to blend with the surrounding original material.
3 layers of a surface coating (acrylic resin) were applied, both to protect the metal from soiling and corrosion, and to seal the spot treatment/corrosion converter, which may otherwise be hazardous to health.