Roman iron coins, coated with a copper alloy, from various places in Austria were investigated. The numismatic term for such a coin is subferrat.
The Cu alloy coating consists of Cu, Pb, Sn, Zn and small amounts of Ag. This alloy is a variant of gunmetal known as “leaded red brass”. Inside the red brass coating droplet-shaped iron inclusions were observed and at the grain boundaries of the iron core copper and lead were detected (liquid metal embrittlement). Probably, the iron coin was plated by immersing it in a molten copper alloy.
In Palfau (Styria/Austria) a bloom was found during archaeological investigations of a historical trade route, the so-called "Dreimärktestraße". As iron smelting sites have not been recorded in the vicinity, the original production site remains unknown; it is assumed that the bloom was lost during transport.
The bloom has a diameter of about 18 to 19 cm and shows corrosion products and stones on its surface. A small fragment was used for metallographic investigations.
The bloom contains many pores and inclusions like oxides and also charcoal used in the metallurgical process. Microstructures from cast iron over steel to pure iron were observed. There are strong carbon gradients in the metallic iron responsible for the various microstructures.
Archaeological excavations of a historical road passing through Palfau (Styia / Austria) revealed a large number of iron artefacts including iron nails.
One of the nails for horse shoes, which measured about 3 cm in length, was prepared for metallographic investigations. The nail exhibits lengthwise cracks, which separate the specimen in two parts with different composition; one part contains less carbon (< 0.2 wt% C) and in the other part mainly pearlite (about 0.8 wt% C) is observed. This carbon gradient and the deformation during forging caused a great number of steel microstructures. Additionally slag inclusions and corrosion products could be observed.
Bloomery furnaces and later the “Stuckofen” were used for iron smelting. A byproduct from the smelting in the “Stuckofen” was a type of raw iron called “Graglach”.
During the transport “Graglach” got lost and could be found during archaeological investigations at the historical trade route, called "Dreimärktestraße".
“Graglach” is metallic iron with variable Carbon content representing steel or cast iron.
Slags from Eisenerz, Austria
Slags from mediaeval iron smelting furnaces were analyses. Depending on its chemical composition the solidification of these slags is different. Three types could be described showing different morphologies of wuestite (FeO, white), fayalite (2FeO.SiO2, light-gray) and glass-phase (amorphous silicates, dark-gray).