Ironmaking in antiquity is described in a report from English Heritage.

Introduction

If a fire of wood is lit on a shallow hearth made of stone the kindling used will first drive the moisture from the wood, which will then burn. As the burning causes the fragmentation of the charred wood, small pieces will accumulate in the bottom of the hearth, where they will become starved of oxygen from the air. If the stone used for the hearth is an oxide or carbonate, as most stones are, the charred wood, or charcoal in the bottom of the hearth will try to take the oxygen from the stone. Some oxides do give up their oxygen to the carbon from the charcoal and what is then left in the hearth will be partly metallic.

Lead, tin and iron may all have been discovered because of this process. Copper had been found in metallic form, but is also produced when its oxide or carbonate is burnt with charcoal. It would not have taken long for the realisation that mixing charcoal with small pieces of the appropriate stone enabled a process to be devised for the production of these metals. None of the stones were pure oxides of a single metal and there was a lot of the oxides of silicon, aluminium, titanium and calcium that would have been mixed in with the product. These metals cannot be made by heating their oxides with carbon, so their oxides remain mixed in with the metals that are produced. Lead and tin become liquid at the temperature of the fire and are easy to separate from the oxides. Iron, which is the subject of this article, does not become liquid at ordinary fire temperatures but forms a porous mass, called a bloom because it looks a bit like a flower. The metal is intermixed with oxides.

Some of the mixed oxides form clinker, which can be separated from the metal by working the hot mass. Other oxide mixtures, particularly those containing calcium oxide - lime - become fluid and stay with the metal as it is worked. These more fluid oxides are removed by hammering the metal, which also squeezes the granules of iron together.

Hammering the hot metal requires power. This would originally have been supplied by men, but at the late period when ironmaking was imported to the Midlands, probably from the Weald of Kent and Sussex, the scale of operation required water power. Like Kent and Sussex, but in distinction to the northern areas, where iron was also made, the availability of water power was limited both by relatively low rainfall and the lack of high hills.

Ironmaking in the Midlands

Where there was adequate water power a leat was constructed from the supplying stream to create a mill pond. In the Sheffield area, for instance, the River Sheaf has a whole series of mill ponds along it successively taking water as the river courses down the valley. In the Midlands it took all of the water in a stream to produce enough power for one operation and the resulting configuration can still be recognised in Cannock Chase, where Lord Paget located the first ironworks to be built in the area. It was similar to the Wealden configuration shown at the left. This picture and the one at the top of the page are taken from the Wealden Iron Research Group's web site. The works were located immediately under the dam forming a lake from a small stream. The purpose of the dam being to concentrate the gentle fall of the land into the biggest step possible so as to generate some power from the fall of the limited water supply.

By the middle ages, therefore, water power had become one essential ingredient of an iron making site. Two others were more important. Firstly the existence of a proximate supply of good quality ironstone and secondly abundant supplies of wood suitable to the production of charcoal.

About six times as much charcoal by volume is required as ironstone, but the ironstone weighs more and with the mud roads of the sixteenth century it was the ironstone that was the more dificult to transport. Lord Paget had ironstone close to his Cannock Chase location and the chase also supplied plenty of wood. The water came from the Rising Brook and the Stoney Brook, supplying two operations on the Chase.

Ironmaking came to the Midlands to support the growing blacksmithing trade. The background to this is described in a page about Birmingham.

Ironmaking at Middleton

Francis Willoughby would have been very familiar with Lord Paget's activities. His association with Lord Paget was the result of the early death of Henry Willoughby, Francis' father, who was killed supporting the Earl of Warwick in putting down Ket's Rebellion in 1549. Lord Paget had acquired the wardship of Francis' older brother, Thomas, thereby gaining access to, and use of the income from, the Willoughby estates. Thomas married Lord Paget's second daughter, Dorothy but he died at the age of eighteen. Francis then became head of the family, but he was only twelve at the time. His wardship was then purchased by Sir Francis Knollys, one of Queen Elizabeth's courtiers.

Henry Willoughby had married the aunt of Lady Jane Grey and when Henry died Thomas was initially fostered by the boys uncle, Jane's father, Henry Grey, Marquis of Dorset and Duke of Sussex. Henry's wife was Francis Brandon the niece of Henry VIII. The attempt by Henry Grey to place his daughter on the throne caused him to lose the wardship of the Willoughby boys, and, of course, his life, but it is evident that Francis moved in very elevated circles when he was young. It may have been this early exposure to power and luxury that drove him into business and into bankrupting the family by his extravagance in building a new Wollaton Hall. He certainly needed a lot of money to achieve his ambitions.

On his Wollaton estate he exploited the sea-coal, which outcropped there and was used mainly for domestic heating until the Industrial Revolution; he also tried but failed to grow woad for use as a dye. He must have looked for ways of raising an income from his Middleton Estates. There is no record of these having any use other than hunting before Francis came along. There was, however, a pool and dam - probably first constructed for fish-farming - and there were trees. His exposure to Lord Paget would have told him that he had two of the three things needed for making iron and in about 1570 he set about trying to do that. Francis Willoughby thus became only the second ironmaker in the Midlands.

  Part processed bloom found in the grounds.

Billet from medieval ironworks, found in
building foundations

He also became the only known operator of a medieval ironworks who did not have control of the primary source of raw material, ironstone. He had first to import it from Walsall, where Lord Paget controlled the market, but later found a slightly closer source at Polesworth. At first the bloomery iron process was used and a hammer mill was powered by the water from the pool to process the blooms and shape the product into the form required by the Birmingham blacksmiths. The bloomery process had been used since Roman times but a more productive process was invented in Germany in the fifteenth century and this was brought to Britain around the turn of the century. This used a blast furnace as seen at the top of this page. It differs from the bloomery process in that the temperature is raised much higher enabling the iron to melt and separate from the gangue. This is achieved by blowing air through the mixture of charcoal and ironstone, producing a hotter fire but it is also because at the higher temperature carbon is absorbed into the iron and this produces and alloy of iron and carbon that melts at a significantly lower temperature than pure iron.

The disadvantage of the blast furnace is that it produces a material, which when cold is also brittle.

Further reading
'The Establishment of the Willoughby Ironworks in North Warwickshire in the Sixteenth Century"; R.A.Pelham, Univ of Birmingham Hist.J.,IV, (1953-4),18-29.
'Sir Francis Willughby's Ironworks, 1570-1610'; R.S.Smith, Renaissance and Modern Studies, XI,(1967),90-140.
'The Development of the Iron Industry in South Staffordshire in the 17th Century: History and Myth'; P.W.King, Staffordshire Archaeological and Historical Society'; XXXIII, (1996-7) 59-76.