Application of colour metallography in the examination of ancient metals

Abstract

The use of colour in the metallographic examination of ancient metals is useful both for research and teaching purposes. Application of different optical methods of examination include: polarized light, with or without a first-order red compensator, and differential interference contrast microscopy (DIC). The use of DIC can be combined with the other techniques mentioned in the text for the examination of etched or unetched metal surfaces, which are best observed microscopically using a metallograph. Colour techniques are now used routinely in industrial metallography, and are available for a variety of metals and alloys. Colour tint etching can be used to enhance grain structure or different phases present in the metallic artefact which may not be visible in conventional etched samples, or which lack optical contrast. Many more applications of these techniques in the examination of ancient metals will be published in the literature as they become better known and second-hand equipment with DIC lenses enter the market at a price suitable for conservation laboratories to purchase them.

Keywords:

• Metals
• Metallographic examination
• Colour etching
• Nomarski plates
• Differential interference phase contrast
• First-order red plate