puddle bar
An iron bar made at a single heat from a puddle ball, by hammering and rolling.
puddle bar: wrought iron rolled from a single heat's work
A puddle bar is a length of wrought iron produced by taking a puddle ball, fresh from the puddling furnace, and drawing it down through successive heats under a steam hammer and rolling mill. The puddle ball, a soft mass of iron and slag roughly the size of a loaf, is hammered and squeezed to expel molten slag, then rolled into a bar shape in a single continuous sequence without allowing the metal to cool to room temperature between operations.
The defining characteristic is that all this work happens within one heat cycle. Once the puddle ball emerges from the furnace at around 1200 degrees Celsius, the ironworker has perhaps 30 to 60 minutes depending on ambient conditions to complete the hammering and rolling before the metal becomes too cool to work. If the bar is not finished within that window, it must be set aside, reheated in a separate heat, and the process restarts. A puddle bar made in one continuous heat is stronger and more homogeneous than metal pieced together from several heats.
Puddle bars were the standard raw material fed into rolling mills throughout the 19th century and into the early 20th. They typically ranged from roughly 2 to 5 inches wide and up to 3 feet long, depending on the furnace capacity and mill size. Mills would receive bundles of puddle bars, reheat them together, and pass them through finishing rolls to produce merchant iron shapes: rails, angle iron, flat bar stock, or rounds for further forging.
A puddle bar could be rolled into various cross-sections while still hot: square, round, or flat. Some were left in rough bar form for immediate sale; others were re-rolled in separate heats to achieve tighter dimensional tolerances or specific profiles. Quality depended entirely on the puddler's skill in removing slag: incomplete expulsion left seams and weaknesses that would fail under load.
Puddled iron and puddle bar production declined sharply after 1890 as the Bessemer and Siemens-Martin processes became dominant. By mid-20th century the puddle bar had become obsolete for new construction, though a few mills continued making them for repair work and niche applications where the ductility of wrought iron remained preferable to mild steel. The term survives today mainly in metallurgical history and in the lexicon of workers who trained under the old system.