David Thomas' success with his hot-blast furnace at Ynyscedwyn soon lead to the expansion of the works, with three furnaces burning local anthracite.
News of this development interested the owners of ironworks in America, where there were also large anthracite deposits. After one of their number visited Ynyscedwyn in 1838, the Lehigh Coal and Navigation Company offered David Thomas (right) an opportunity to develop an ironworks in Pennsylvania.
Thomas emigrated with his family in June 1839. He was so successful in America that he founded his own Thomas Iron Company at Hokenauqua, which soon became the biggest anthracite iron producer in the USA.
Back in Ystradgynlais, George Crane continued the work there, eventually having six blast-furnaces working with a thousand men working on the site. He also bought five local coal mines to keep the furnaces supplied, employing 240 men.

After George Crane's death his son continued the ironworks, but by the 1850s production was overshadowed by the larger ironworks at Ystalyfera.
New methods were invented elsewhere, and Ynyscedwyn ironworks went into decline. By 1870 it had only one working furnace, and later plans to build a new ironworks were abandoned leaving the arches of the unfinished building standing.

More on the story of iron smelting...