Short answer
Cast iron is a family of relatively carbon-rich iron alloys associated with casting. Traditional wrought iron is low-carbon iron containing characteristic slag inclusions and worked into shape. Their internal structures help explain why traditional wrought iron can be bent and forged, while ordinary gray cast iron tends to fracture with relatively little deformation. 1 2 3
The word traditional matters. Decorative metalwork sold or described as “wrought iron” may actually be mild steel. And cast iron includes several material types, so the behavior of gray cast iron should not be assigned to every member of the family. 1 2
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At a glance
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| Question | Cast iron | Traditional wrought iron |
|---|---|---|
| General composition | Iron-based alloys, commonly above about 2% carbon. | Predominantly iron, low in carbon, with slag inclusions. |
| Characteristic structure | Varies; gray iron has graphite flakes, ductile iron has rounded graphite. | Slag inclusions are often stretched along the working direction. |
| Traditional shaping | Molten material solidifies in a mold. | Hot working, such as hammering or rolling. |
| Typical behavior | Gray iron is relatively brittle; other types can be much more ductile. | Generally workable and ductile. |
| Does ornament prove identity? | No. | No; worked steel can resemble it. |
| Can it corrode? | Yes. | Yes. |
Sources: classification and graphite forms 2; traditional ironwork 1; material analysis 3.
What each thing is
Cast iron
Cast iron names a material family, rather than simply any iron-containing object made in a mold. Carbon content is generally higher than in ordinary steels, and silicon is an important ingredient in many types. Gray, ductile, white, and malleable cast irons have different structures and properties. 2
Wrought iron
Traditional wrought iron has a low carbon content and usually contains slag, including iron silicate inclusions. Working the material elongates many of these inclusions, producing its characteristic fibrous structure. It is therefore not chemically pure iron. Historic wrought iron could be produced through more than one process; the material name does not specify a single manufacturing recipe. 3
Key differences
The internal structure affects deformation. In gray cast iron, graphite flakes create weaknesses that help cracks develop. In ductile iron, graphite is more rounded, allowing a much more favorable combination of strength and ductility. Wrought iron’s working history instead leaves elongated inclusions within the iron. 2 3
The forming methods leave different possibilities. Casting allows a pattern to produce repeated, intricate shapes. Traditional wrought iron can be hammered into scrolls and joined using methods such as forge welding, collars, and rivets. These are useful historical clues, although replicas and later repairs complicate identification. 1
The names do not give a complete engineering assessment. Composition, structure, deterioration, and the particular component all matter. Knowing that a railing is “iron” does not establish its material or structural condition. 1 3
How to tell them apart
Start with records, maker information, or an existing specialist material assessment. Repeated cast details and evidence of hand working can suggest a manufacturing route, but cannot reliably identify every component. A decorative scroll may be steel, and an assembly may contain several materials. 1 3
Where the distinction affects conservation or repair, examination of a prepared sample can reveal graphite or slag structures. Historic England used metallography and electron-microscope analysis to distinguish materials in the Elmore Court gates. That is a much firmer identification than an object’s shape or color. 3
Where they overlap
Both are predominantly iron-based materials, and both have been used for architectural details and structural work. Both can corrode. A historical object can combine cast pieces, wrought pieces, and later steel additions; the category need not apply uniformly to the whole object. 1 3
Edge cases
Ductile iron is still cast iron. Rounded graphite particles distinguish it from gray iron and improve ductility. “Cast” does not automatically mean equally brittle. 2
Malleable iron is also cast iron. It is produced by heat-treating suitable white-iron castings. The adjective malleable does not make it wrought iron. 2
“Wrought iron” may name an appearance. Historic Environment Scotland specifically cautions that the term is often applied to worked steel. Ask whether the description identifies a tested material or a style. 1
Why the distinction exists
The names reflect different ways of producing and shaping iron materials. Casting supported repeated designs made from patterns; working low-carbon iron supported bending and forging. As steel became widely available, it could replace wrought iron in some work while familiar decorative terminology persisted. 1 3
Common misconceptions
- “Wrought iron is pure iron.” Its characteristic slag inclusions are part of the distinction. 3
- “All cast iron behaves like gray iron.” Ductile and malleable types differ substantially. 2
- “A handmade-looking gate must be wrought iron.” Worked steel can have the same style. 1
- “One gate has one material.” The Elmore Court analysis found several. 3
Examples
A repeating cast ornament illustrates the use of molds; a documented wrought-iron scroll illustrates hot working. Those appearances are clues, not conclusive tests. The Elmore Court gates provide a documented example: sampled components included cast iron, wrought iron, and mild steel. 1 3
Sources
Sources checked October 3, 2026.
- Historic Environment Scotland, Engine Shed — Iron. Traditional ironwork, forming, and terminology.
- TWI — Weldability of materials: cast irons. Material families and graphite structures.
- Historic England — Analysis of samples taken from the entrance gates at Elmore Court, Gloucestershire. Definitions and examination of actual components; 1998 report.