The first project for second-year metals conservation students
is on ferrous metals. I received this Japanese tsuba encased in
ferrous corrosion that has badly damaged the fine detail and had
also consumed the gilding of this piece.
The dating of this object is difficult as designs and styles
varied from maker to maker. The entire of the object is chased and
engraved iron with damascening and amalgam gilded decorative
highlights, with inclusions of gold, silver and copper alloy
Under the microscope you can see the potential for detail
beneath the corrosion. A simple meticulous mechanical clean with a
solvent and a scalpel blade underneath the microscope revealed the
original detail of the piece.
During the cleaning process I noticed that there was a
corrosion-coloured waxy layer in the low points of the
Removal of this was difficult because solvents just moved the
residue about, which made more unnecessary work and started to
damage the gilding in the background, which had been completely
encased in corrosion.
The iron was then stabilised with a chemical corrosion
inhibitor of tannic acid 10% solution and 0.01% phosphoric acid. A
minor pigmented protective coating of microcrystalline wax was then
applied to prevent further corrosion.