Zinc coatings of Indian plate and mail armour
Metallic coatings are commonly found on iron and steel armour and range from gold and silver to tin and lead. Sometimes the coatings are primarily decorative in other cases it is purely practical, preventing corrosion. A group of Indian plate and mail Armours, known from inscriptions to be earlier than the 1680s, appeared to have traces of a grey oxidized metal. Could qualitative XRF analysis discover the composition and extent of this?
Results of analysis
The mail and plate armour shown (XXVIA.300) and many other examples were found to have been coated in zinc, probably by hot dipping into the molten metal. XRF was able to show this treatment was far more extensive than the limited visible traces.
These Indian armours show the earliest known evidence for galvanising, a process for which the first European patent was from 1836 in France. As with modern galvanising the zinc protects the iron in two ways. Firstly, it acts as a physical barrier to air and moisture. Secondly, because zinc is more electrochemically reactive it provides sacrificial protection to the iron. Such rust proofing would have been highly desirable in a tropical climate.
This research project was written up as an undergraduate thesis by Helen Bowstead Stallybrass at the Department of Archaeological Sciences, Bradford University and also formed a major part of an article on these armours in the Royal Armouries Yearbook Vol 5. Without prior XRF analysis there would have been a danger that this important evidence would have been damaged and eventually lost during cleaning. The results have been forwarded to other museums which own similar armour.