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- A furnace consisted of two main parts, the lower one called a pit and the upper called a shaft. A hollow was a simple hole dug out in the ground; it had 40-45 cm in diameter and not more than 50 cm in depth. Its main function was storing of slags coming from the reduction zone.
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From the Iron Age and Saxon periods, ‘slag-pit’ or ‘non-tapping’ furnaces are known, such as the probable Pre-Roman example from Levisham Moor, North Yorkshire. During the smelt, the slag gradually drained into a pit beneath the furnace and cooled there, either as numerous small runs and lumps or as a large block of slag upwards of
Dec 1, 2011 · Two kinds of furnace were identified in the works, the 'slag-pit' type and the 'tapping' type, the former being the earliest known British type, the latter being a Late Iron Age innovation that remained in use into the post-medieval period.
- Introduction
- Principles of Early Iron Smelting – Bloomery Process
- Determining Typologies: What Is A Bowl Furnace?
- Experimental Reconstruction
- Methodology
- Results
- Microscopic Analysis of Materials and Results
- Discussion
- Conclusion
The bowl furnace is a somewhat enigmatic feature within the early history of iron-making. Site formation processes and preservation can mean that the material evidence found for shaft furnaces sometimes reflects a truncated design, and therefore may resemble what is thought to be a bowl furnace. The bowl furnace design was rejected by many in the 1...
The fundamental principle of iron smelting is the reduction of the metal oxide with carbon dioxide, which is provided by partial combustion of the fuel, in this case charcoal, with air from the tuyère (Tylecote, 1986). It is necessary for the air from the tuyère to pass through a sufficient amount of charcoal before there is enough carbon monoxide ...
Variously, throughout the 1950’s to the 1980’s, many different classifications of early furnaces were attempted. In these, the bowl furnace appears in a range of different forms, from rudimentary holes in the ground, to what are essentially small shaft furnaces. The size and covering of these furnaces are varied, but the basic form is of hollow in ...
Owing to the somewhat limited research and literature on the use of the bowl furnace to make iron, an experimental project was designed to add more data to this field of research and to evaluate the success of the bowl furnace at producing iron. The experimental campaign consisted of comparing two different methods of loading the ore into the furna...
The furnace was reconstructed to represent a general model of a bowl furnace, rather than aiming to reconstruct a specific example from the archaeological record. The design (See Figure 2) was most similar to Tylecote’s (1986) Type (B). The pit for the furnace was dug into the ground, to provide a slag pit, which is the area below the tuyere. The d...
Smelt One The first smelt produced a friable conglomerate which can be seen in Figure 7 Small foils of malleable iron were noted on the surface of the conglomerate although these were too small to constitute ‘useful’ amounts of iron. This does however suggest that the reducing conditions required had been achieved. The disassembly of the furnace sh...
Samples were taken from the three different areas of the conglomerate formed in the first test firing (See Figure 7) and examined using reflective light microscopy. The samples were mounted in epoxy resin, then ground using an automatic Buehler Metaserv machine using 120 to 4000 grit papers. The samples were then polished using an automatic Buehler...
The results of the experimental campaign demonstrates that the furnace conditions within a bowl furnace of this size and shape, are capable of being sufficiently reducing to produce an iron bloom and to reduce iron oxide to iron metal. This campaign was successful in producing very small amounts of iron. Further experiments to investigate the effic...
This consideration of the bowl furnace for iron smelting – combining analysis of previous experiments conducted with the experimental campaign presented in this paper, has demonstrated that there is still more to be understood about the functioning of a bowl furnace for iron smelting. We believe that we have shown the value in further experimental ...
Nov 22, 2020 · Vertically flowing melts are to be designated as tap slags as well, which are formed by smelting of iron ores in deepened pits below shaft furnaces. Such slag-pit blocks, dating from the late Latène period to the Roman Empire, are described in detail from Joldelund in northern Germany (Ganzelewski 2000), but are spread over the entire northern ...
- Andreas Hauptmann
- 2020
Although since then these furnace bottoms have been identified as the waste of iron-smithing and, more recently, the slag-pit furnace recognised as the predominant early Irish iron furnace type, the bowl furnace has proved tenacious and still appears in the literature.
- Paul Rondelez
Oct 1, 2019 · Two main smelting technologies are recognised for iron bloomery smelting, characterised by the way the slag was removed from the active part of the furnace; non-tapping furnaces and tapping furnaces ( Cleere, 1972; Paynter, 2007 ).
In a slag-pit furnace process only barren rock was melted which together with not fully reduced ferrous oxides created liquid slag. It was calculated that in order to obtain a block of slags weighing about 100kg about 200kg of ore needed to be melted and 250-300kg of charcoal to be burned.
