A finery furnace (also called finnery or “finoven” in Dutch) is a traditional furnace in which pig iron from the blast furnace was refined into wrought iron. The process was used in the Middle Ages and the early Industrial Revolution to produce construction iron, tools, gates and weapons. The finery furnace disappeared around 1900 with the rise of modern steel mills using the Bessemer and Siemens-Martin processes.
Operating principle
In a finery furnace pig iron was stripped of carbon and impurities:
- Lumps of pig iron are placed in the furnace above a charcoal fire
- Air blasts raise temperatures (1300–1500 °C)
- Oxidation — carbon, phosphorus and sulphur burn off or slag away
- Bloom formation — iron becomes tough and malleable
- Forging — the bloom is hammered under a water-powered hammer into bars or plates
The end product, wrought iron, was stronger and more deformable than pig iron — perfect for building construction.
Significance for construction history
Wrought iron from finery furnaces was used for:
- Railings and balconies — ornate wrought-iron decoration
- Tie bars and anchors — for tying masonry walls
- Bridge structures — early iron bridges (18th–19th century)
- Stair railings and lanterns — street furniture
- Hoist beams and hardware — durable mechanical parts
- Nails and fasteners — hand-forged
Famous examples of wrought-iron architecture include the Eiffel Tower (1889), old railway station roofs and Art Nouveau balcony railings.
In heritage conservation
When restoring listed buildings, wrought iron from old finery production is treated carefully:
- Material identification — analysing carbon and slag content
- Conservation — preventing corrosion without altering the original
- Replacement — replicas forged by specialist smiths
- Authenticity — wrought iron has a unique fibrous structure
Difference from steel
- Wrought iron — low carbon (<0.1 %), fibrous structure, forged
- Cast iron — high carbon (3–4 %), brittle, cast
- Steel — medium carbon (0.1–2 %), rolled, castable
Related terms
- Wrought iron
- Steel
- Construction metal
- Anchor
- Bronze
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