Ynyscedwyn* Ironworks
(* Different spellings of the name appear to have been used at different periods....
Ynyscegwen, Ynysgedwen and now Ynyscedwyn )

Iron has been made in the in the vicinity of  Ystradgynlais since at least the early 17th century. For hundreds of years wood charcoal had been used for smelting iron, but wood charcoal was expensive and always in short supply and in 1709 Abraham Darby, in Ironbridge, Shropshire, had begun to use coke as a replacement. This improved the process and allowed larger items with thinner walls to be cast, thus expanding the use of the technology whilst also reducing the cost.

Foundry coke, as it became known, was made by blending soft bituminous coal with anthracite and then heating it in an oven in an absence of air to drive off the volatile matter. Although soft coal and anthracite were available in quantity they usually occurred in different locations and had to be transported. The Swansea Valley was rich in anthracite, but it had no soft bituminous coal, and the construction of the Swansea Canal in 1794 was vital for transporting supplies of coal and ore to the valley's burgeoning iron industries. The coking process itself was also a slow and costly operation which produced lots of pollution.

In 1820 a David Thomas began his own experiments at the Ynysgedwen*  Ironworks in Ystradgynlais, using only local anthracite, with a view to reducing or eliminating the need for coke. He modified a Cupola Furnace fitted for Hot Blast (as patented later by Neilson in 1828).

George Crane, the owner of the ironworks, recognised the significance of this process and on 5th February 1837 the first furnace to be successfully fuelled by anthracite was "blown-in".

This led to an ironworks building-boom with 36 furnaces being constructed in and around the South Wales anthracite belt in the following years. Ystradgynlais itself grew from a population of 993 in 1801 to 3758 in 1851.

David Thomas was born in the Swansea Valley in 1791. When he was 17 he went to work at Neath Abbey Ironworks, the most advanced producer of steam engines and associated heavy machinery in South Wales. 

By 1817 he was travelling throughout England and Wales erecting pumping engines and it was at that time he was appointed Superintendent of the Ynysgedwyn Ironworks.

In 1839 he received an offer from the United States and emigrated there to build an anthracite fuelled blast furnace in Lehigh County, Pennsylvania. Most accessible reserves of coal in the USA were anthracite and David Thomas had the know-how to utilise this resource in the production of iron. 

In 1854 he founded the Thomas Iron Company, which became the largest producer of anthracite pig-iron in the United States and he is remembered as David "Papa" Thomas, the father of the American iron industry.

By 1860 Ynysgedwyn Ironworks was employing 1000 men and operating seven furnaces, but by 1872 it was closed, outdated by new plant and technology. The site was then used as an iron foundry and later by The Welsh Tinplate Company. It was finally abandoned in 1947.