The iron pillar at Delhi has attracted the attention of archaeologists and corrosion technologists as it has withstood corrosion for the last 1600 years. Proponents of the environmental theories state that the mild climate of Delhi is responsible for the corrosion resistance of the Delhi iron pillar. On the other hand, several investigators have stressed the importance of the material of construction as the primary cause for the pillar's corrosion resistance. This is primarily due to the high P content of the iron produced during these times. The addition of P was intentional as iron produced during earlier times does not show the presence of P. To understand the precise reason for the corrosion resistance of the Delhi iron pillar, we analysed the composition of the rust on a Gupta period corrosion resistant iron clamp and also the rust on the Delhi iron pillar.
Archaeometallurgical studies form a small component of our research activities.
We summarize below some of the exciting results of our study. The present study also provides valuable insight into the corrosion resistance of steels. The microstructure of the iron of the Delhi iron pillar is typical of wrought iron. Iron was produced in ancient times by solid-state reduction of iron ore using charcoal and after the reduction process, the slag particles in iron were squeezed out by hammering. This invariably resulted in the presence of slag particles and unreduced iron oxide in the microstructure.