Coalbrookdale Museum of Iron, Ironbridge - October 28, 1977
The Old Furnace seen before the cover building was erected to protect the historic structure.
The Old Furnace began life as a typical blast furnace, but went over to coke in 1709. Abraham Darby I used it to cast pots, kettles and other goods. His grandson Abraham Darby III smelted the iron here for the first Ironbridge, the world's first iron bridge.
The lintels of the furnace bear dated inscriptions. The uppermost reads "Abraham Darby 1777", probably recording its enlargement for casting the Iron Bridge. It is unclear whether the date on one of the lower ones should be 1638 (as it is now painted) or 1658 (as shown on an old photo).
The interior profile of the furnace is typical of its period, bulging around the middle, below which the boshes taper in again so that the charge descends into a narrower and hotter hearth, where the iron was molten. When Abraham Darby III enlarged the furnace, he only made the boshes wider on the front and left sides, but not on the right where doing so would have entailed moving the water wheel. The mouth of the furnace is thus off-centre.
Iron was now being made in large quantities for many customers. In the 1720s and 1730s, its main products were cast-iron cooking pots, kettles and other domestic articles. It also cast the cylinders for steam engines, and pig iron for use by other foundries.
In the late 18th century, it sometimes produced structural ironwork, including for Buildwas Bridge. This was built in 1795, 2 miles up the river from the original Ironbridge.
Due to advances in technology, it used only half as much cast iron despite being 30 feet (9 m) wider than the Ironbridge. The year after that, in 1796, Thomas Telford began a new project, Longdon-on-Tern Aqueduct. It carried the Shrewsbury Canal over the River Tern and was supported by cast-iron columns. Charles Bage designed and built the world's first multi-storey cast-iron-framed mill. It used only brick and iron, with no wood, to improve its fire-resistance. In the 19th century ornamental ironwork became a speciality.
