Copper-Coated Roman Coins – Subferrati

Abstract

Abstract In the third century AD, replicas of small denomination coins were manufactured in the border areas of the Roman Empire. They are composed of an iron core with a non-ferrous metal layer and are called “Subferrati”. Four roman coins, one of them from Loig, two of them from Enns, and one of them from Magdalensberg, were metallographically prepared and examined in the LOM, SEM-BSE, and by means of XRF. The non-ferrous metal layers are composed of lead-containing bronzes with segregation structures from a α-copper solid solution, Sn-rich δ-phase, and Pb. Spherically shaped iron inclusions could also be observed in the bronze coating. They can be attributed to the fact that the iron core was dipped in liquid bronze. The coins' iron cores mainly contain ferrite and little pearlite. Elongated inclusions originate from the iron manufacture in the bloomery furnace and subsequent forging. The Neumann lines are in the ferrite formed during minting. Copper could also be observed on the ferrite grain boundaries (so-called liquid metal embrittlement) which suggests a contact of the liquid non-ferrous metal with the iron core. Based on the present results, no indications of different mints or other coating methods could be found.