Iron ore has been mined and smelted in our area for thousands years, even before the Romans arrived. We know this because of the abundance of slag or cinders to be found locally.
Iron ore would have initially come from from several mines on the Doward some of which are overlooking the Wye and can still be seen and entered today. Later perhaps some mines from further afield.
Being made from clay the very early bloomery furnaces themselves have not survived. Bloomery furnaces burnt charcoal to heat the iron ore but were limited to a relatively low temperature of about 800 degrees C. Old drawings depict some furnaces incorporating hand operated bellows which probably produced higher temperatures, although this was not always used. Smelting iron ore in this way to converted it into ‘bloomery’, a mixture of iron, impurities and slag, which needed repeated re heating and hammering to refine it into a useable product.
Here is an activity that would suit me and perhaps some other WAGLHS members.
The product from a bloomery furnace was a somewhat impure form of iron removed from the furnace as a rough, semi solid lump. It was a very inefficient process and the waste product hardened into a shiny black slag called ‘cinders’ which still contained 40% to 60% iron in some cases. Sometimes a higher percentage than the raw iron ore. Cinders were produced in vast quantities in the middle ages and just dumped in heaps often 20 feet high in places. Cinder Hill Street in Monmouth derives its nome from them. Cinders can be found today in gardens in Whitchurch, Sellarsbrook and under old railway tracks and roads where it was used as ballast. The island in the river Wye at Symonds Yat was once known as Cinder Island and was reputedly built of dumped iron bloomery and slag. Although it was certainly not always an island the dump was most likely once on the river bank. It may even been used to form the base of ‘New Weir’, the weir that once spanned the Wye here. There is still plenty slag and bloomery to seen there on the shore today.
In 1685 New Weir Forge was constructed by Mr George White and is is famous locally but there is no record of iron ore smelting carried out in his works. This amount of cinders suggests that it was also the site of much earlier iron works using water power generated from the river.
The site once known as Vagas field is approximately where the North bound services on the A40 in Whitchurch is today. Well before the dual carriageway was constructed there was archaeological evidence of a great cinders pit existing here. Roman artefacts found buried in these pits are indicative of a large Roman smelting operation here almost here in our village.
A bloomery furnace could built and operate more or less wherever the raw materials, ore and timber, were plentiful and this had almost certainly had been going on for over two thousand years. In these early days the iron produced was not liquid enough to flow would have been removed from the furnace as a soft lump containing some slag encasing the very impure iron called bloomery. It then had forged, repeatedly re-heated in a separate furnace or hearth, and beaten with hammers, to remove some more of the impurities until it eventually turned into a usable form of iron. But the quality was still not good enough for many purposes.
Later ‘Puddle Furnaces’ produced a more refined iron direct from iron ore and also from the iron the iron rich cinders, the wast product from earlier furnaces. In this process the fuel was burnt separately from the bloomers or cinders and to a higher temperature, producing molten iron which collected in the ‘puddle’ or ‘hearth’ in this picture.
Soon the demand for iron products grew requiring much higher outputs than this process could supply. This in turn needed larger amounts of air power which, in the days before steam engines, could only be generated by water and so the process had to be attached to a water mill which it meant being re-located beside a river or stream.
Smelting at higher temperatures to 1,000 degrees C’ and more required a much improved design of furnace with a more heat resistant lining and greater quantities of forced air but it produced a far better quality iron. Small quantities of lime acted as a flux and sometimes small amounts of water were added to improve the iron extraction resulting in a much more pure and fluid, molen iron that could be ‘run off’ as a liquid directly into molds solidifying into either as flat ‘plates’ or ‘pigs’ – Pig Iron, who’s shape vaguely resembled a sow feeding piglets. By the fifteenth century, if not earlier, furnaces were all using using this method and with much larger and more powerful bellows, usually two of them. As methods and designs improved furnaces using much higher air blast became known as blast furnaces. The waste product now contained far less iron. Cinders could be easily obtained from old dumps without mining and were often added to iron ore in the smelting stage.
The resultant plate or pig iron was of a size that was easy to handle and transport. It was not only sent to local smiths but also tranported large distances to other industrial centres where iron or steel products were made by forging or casting. Iron from different areas contained slightly different chemicals making it more malleable, harder or more suitable for different end products.
The next stage was forging, also carried out locally. But this is another story.