Late Antique Blast Furnace Found in South Tyrol

[Eleatic Guest]

Archaeologists found a blast furnace near Brixen, South Tyrol, dating it to (more than) 1500 years ago. The smelting site on the Säbener Berg had 15 shaft furnaces, several of which have been found to produce cast iron. Curiously, the iron ore wasn't mined at the site but had to transported from further away. The ironworks covered an area of 320 sm that were excavated and stratigraphically analysed. The find adds to a small, but growing corpus of evidence that blast furnaces were used by late antique and medieval smiths long before they became common at the turn to the early modern era.

Source: https://www.scinexx.de/news/archaeologie...in-europa/ and here

[Robert Vermaat]

Interesting!

[Sean Manning]

I did not know this study by Hans-Peter Kuhnen!

People who experiment with simple furnaces sometimes create cast iron accidentally (just like its easier to make a lump which is part steel than a lump of nothing but nice soft malleable iron).

I believe that a number of traditional high-temperature furnaces uses hills to get access to fast-moving air above ground level without building high smoke stacks. That would be one reason to put the furnace in Säben on a north-south Alpine pass (the valley south of the Brenner Pass), but I would want to read the study by Hans-Peter Kuhnen and why he thinks the cast iron was deliberately produced. Journalists have trouble with technical and natural-scientific topics and university press-release offices sex things up.

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It might be worth asking Helmut Föll about this although I think Hans-Peter Kuhnen published after Föll retired.

[Eleatic Guest]

Kuhnen writes in his article (p. 29-30) that they conducted an archaeometallurgical analysis on the slag in 2020 and found it to be created in a blast furnace ("Floß- oder Hochofen"), that is one that was able to reach temperatures of 1400 to 1500 degree celsius as opposed to a simple furnace ("Rennofen") whose upper limit was 1200 degrees.

[Sean Manning]

That upper limit was made up by people who did not have experience with low-tech furnaces. As experiments improved, it turned out that people playing around with simple furnaces sometimes made cast iron by accident.

This is a topic where a lot of the printed research is a generation behind what people without PhDs know from empirical experience and have written up outside academic journals (or in technical metallurgical publications which most archaeologists don't read) https://www.leesauder.com/smelting-research The broad books can be especially misleading because they are decades old. It is very hard to write about correctly unless its a research focus and unless you get your hands dirty building furnaces and stoking them.

[Sean Manning]

My understanding is that if you want to make cast iron a stage in your workflow, you need to design the furnaces accordingly, but many teams who have fired up simple iron smelters a few dozen times have made cast iron by accident. Whereas old theoretical research presented wrought iron, steel, and cast iron as three steps which require increasingly sophisticated furnaces, today with more practical experience we understand that workers were often trying to make soft wrought iron because its easy to forge, and trying not to make cast iron because they were not ready to cast it into anything useful.

Running a low-tech iron furnace is like running a kitchen, sometimes the environment does not cooperate and sometimes the materials are not as desired and there are many different ways to the same result. If all that the kitchen produces is Thai food, that could be all the workers know how to make, or it could be what they are getting paid to make today.

[Eleatic Guest]

The archaeologists sent the iron slag to the Curt-Engelhorn-Zentrum für Archäometrie Mannheim to be analysed and maintain that some of the different types of furnaces could have been used for the typical production sequence of cast iron (p. 33). The cast iron slag was found in some of them. They conclude that the evidence is such that it safe to assume that a blast furnace was operated there ("Damit kann als gesichert gelten, dass die Bewohner des Berges in der Spätantike in dem großen Steinbau des Grabungsareals Zinnenmauer eine Eisenschmelze betrieben, um in einem mehrstufigen Arbeitsprozess Eisenerze nach dem indirekten Verfahren zu verhütten.")