It’s a bright spring morning, and I’m stuck in stalemate. My taxi is refusing to budge, and neither is the red-faced man in front of us, waving his arms out of his Toyota window. The two cars are nose to nose on a single-lane country road which was never meant for more traffic than one man and a few sheep. Lined by dry-stone walls, there’s little room for manoeuvre. So I sit and wait until one of them relents, and reverses back up the winding road to a lay-by.

It’s the final leg of a journey which started at 5:45 in London. Two trains, one bacon sandwich and a strong coffee later, and I’m almost at the AGA factory outside Telford – in the Ironbridge Gorge – the birthplace of Britain’s Industrial Revolution.

After a lengthy reverse we’re moving forward again. And as we wiggle into the village of Coalbrookdale signs of its industrial heritage crop up on every street corner: cast iron guttering, cast iron gates, even cast iron curb stones. We drive past workers’ cottages, down Carpenter’s Row and past the Foundry Master’s house, which is now a B&B.

It’s easy to picture Coalbrookdale in its late-eighteenth century heyday. It’s still all grey stone and iron. No red brick and chrome. But back then the quiet Shropshire village was buzzing with 4,000 factory employees and their families. The churches and chapels which stretch up the hill indicate the different denominations of workers who came from far and wide to the industrial hub.

Coalbrookdale has attracted iron workers for centuries thanks to its wealth natural resources: iron ore, coal and water from the nearby Severn. In the early 1700s local industrialist Abraham Darby I became the first person to smelt iron using coke (dried-out coal), which created a drier burn without bubbles, and made a far higher quality iron than anything anyone had seen before. Darby I rebuilt Coalbrookdale Foundry, and started churning out cast iron cooking pots which was, at the time, a complete revelation. Before then, the rich owned expensive brass pans, while the poor used terracotta or clay pots which broke very easily. The cookware was an huge success and allowed Darby I to embark upon more ambitious projects.

The foundry diversified into railway tracks, and then the world-famous Iron Bridge. It made the gates for Hyde Park, and embraced the Art Deco period with cast iron deerhound-leg-tables and intricate ivy and lily-patterned chairs. During WWI Coalbrookdale foundry made aeroplane parts and bombs. But it’s what happened in the factory after the war which has brought me north. In 1929 the AGA arrived in Britain.

AGA isn’t without its own fascinating history too. The iconic oven was invented by Nobel Prize-winning scientist Dr Gustaf Dalén. After being blinded during an explosion in his laboratory he started spending more time at home, and was astounded how his wife and maid were tied to the oven, struggling to regulate its temperature. In a bid to free them both of domestic drudgery he set about inventing an oven which held its temperature more consistently, and so the AGA was born.

Over the years the design has evolved, but the unique concept stays the same. In an AGA, the food is cooked using radiant heat from the cast iron casings, rather than hot air which is the method employed by today’s fan ovens. An AGA might be fueled by gas or oil, or electricity. Whatever the source, it heats the metal, which holds its temperature and indirectly cooks the food.

The concept is straightforward. But as I am guided round the factory, I realise that the actual assembly of an AGA is anything but simple. The tour starts in the pattern room where a team of draftsmen are at work – all omnigrid rulers and nubs of pencils sharpened with craft knives. An AGA is essentially built like meccano, meaning that every component has to be carefully designed to slot into place. “Every 42 mm there’s an extra 1mm added to take into consideration the contraction of the cast iron,” one of the guys explains.

The patterns are made into wooden moulds, which are then turned into aluminium moulds, which are then used to churn out sand moulds. The only way to get any piece of cast iron out of a mould is to break it. So every single component of an AGA has its own sand mould which is smashed once the piece is formed. The sand is collected, cleaned and reused in AGA’s £3.5 million sand cleaning plant. I’m starting to understand exactly why the ovens don’t come cheap.

Next I’m introduced to Phil who is first in to switch on the blast furnace at 4am each morning. We meet by a heap of scrap, where break discs and drain covers pile up in a metal bonfire. “We buy scrap iron from anywhere we can,” Phil explains as he sees me examining the eclectic collection. Since production began, 70% of every AGA has been made from previously-used material. Indeed, scrap is sometimes bought from Aga owners who are trading in an old model. They’re given £1,500 towards a new model, and the old one is taken away to be melted down. “Inside every new AGA is a bit of an old one,” Phil grins.

Once the blast furnace is fired up, scraps of iron, coke and limestone are layered together in the furnace and heated to over 1500°C. Streams of the molten metal are hand-poured into the moulds, throwing light on the factory walls. It’s all hands and tools, human bellows and activity. Very few robotics, but local skills which have been honed over hundreds of years. I’m introduced to a father and son team working side by side. There are 13 members of the Goodwin family working at Coalbrookdale factory on the day that I visit.

Once the moulds have been filled and cracked, every piece is hand-finished to prepare it for the enameling. Hulking tools operated by hulking men who shave away the rough surfaces. They’re twisting and turning the sheets of cast iron as if it were a canvas. “Pick one up,” one of the guys challenges me. Bending my knees and using both hands to lean against it, I struggle to lift it more than a few inches off the ground. He laughs, and takes it off me in a single, swift motion and gets back to filing down a rugged edge.

The bright enameled colours have helped make AGA such an iconic brand. While black ranges hide in kitchen corners, and built-in chrome ovens slide out of sight in kitchen walls, an AGA is often the centerpiece of the room. Traditionally AGAs were conservative creams, racing green and pillar box red. But pinks and lavenders, jades and duck egg blues are making up the a new palette.

It’s in the Ketley factory, nearer Telford town centre, where this accessorising takes place. The AGA pieces arrive in matt cast iron, but are transformed over a three day process which beings with three layers of fused glass, clay and coloured pigment being hand-sprayed onto the castings. Once enameled, the AGA pieces are checked by quality control, and are then separated into the ‘traditional’ and ‘new generation’ models.

The ‘traditional’ models are still constructed in family’s homes by a skilled team. But the vast majority of the factory is now dedicated to the ‘new generation’ models which are built on site. It means that the instillation takes an hour rather than a day, and that the owner can easily take the AGA with them if they move house.

The ‘new generation’ models have lots of other features which set them apart from the AGA which most people know. They can be powered by electricity (rather than the traditional oil or gas models), and can be operated in a way that suit different peoples’ lifestyle. While the ‘traditional model’ is designed to be on nearly all of the time – pumping out heat to warm a farmhouse, for example – the ‘new generation’ AGAs are programmable, so they might be set to turn on between 0600-0800 and again between 1800-2000, perhaps on all weekends when families are at home, or off all weekends when families are away on holiday. Also, each oven can be operated independently. It gives cooks more choice. They might only have  the baking oven on over summer, or just the hobs on during the day time.

The ‘new generation’ AGA is, in many ways, a total change of tack for such a traditional company which was centered round one core product. But the new models weren’t the result of decades of planning and long discussions. They were a quick fire response to a rapidly-changing market. In 2009 AGA’s sales slumped 20%. The brand looked in jeopardy, as did the 250 jobs in the Telford factory. “It was a perfect storm” one of the employees tells me, describing how a very public attack by Guardian journalist Monbiot coincided with wide publication of rising energy prices, and the recession kicking-in, and kicking-out luxury purchases.

The new generation AGA addressed the critics’ issues surrounding an oven which pumped out heat 24/7. The company has also opened itself up to a new customer base. Big, ‘traditional’ models would never have had a place in urban apartments. But now models like the new City60 are really dinky and fully-controllable, opening up ‘cooking through radiant heat’ to a whole new market. The plan is certainly working. While a small corner of the Ketley factory is dedicated to the traditional models, rows upon row of the ‘new generation’ AGAs queue up, ready to be sent to homes round the world.

Not only have the ‘new generation’ models ensured that the company remain a big player in twenty-first century kitchens, but they have helped ensure the future of industry in this part of Shropshire, meaning that the Goodwin family, and many others, will have the opportunity to introduce new members of its clan to the Coalbrookdale Foundry in generations to come.