Four years on, Blenheim Forge is making some of the finest knives in the country – prized possessions in many a knife roll. Hugh Fearnley-Whittingstall and Nigella are both big fans, as is journalist and knife-obsessive Tim Hayward. Argentine celebrity chef Francis Mallmann walked into the forge and bought a job lot one afternoon. These are not just beautiful objets d’art – they’re precise kitchen tools, designed for regular use.

That precision all starts with what seems a rather brutish, imprecise process. That image of a gruff blacksmith, hammer in hand, sparks flying as he pounds away at a blazing lump of metal – it’s not all that far from today’s reality. ‘We actually tend to use a power hammer rather than a traditional hammer,’ says Rich. ‘It’s just quicker and more efficient, but occasionally we do a bit of hand-forging here.’

The knife begins life as a billet – a solid block of metal, where a high quality core layer is sandwiched by two protective layers. At Blenheim Forge, they use Japanese Aogami, or ‘Blue Paper’ steel – an extremely hard carbon steel that can hold a razor sharp edge, but is still relatively easy to sharpen.

Hammer in hand, Rich explains the forging process to me: ‘We start by welding the layers together by getting them really hot and putting them through a rolling mill, which is like a giant pasta machine but for metal. The mill presses the layers together and fuses the metal into one piece. After that, we cut off a section of the metal and forge the geometry onto the blade.’

He shrugs. ‘It sounds complicated, but it’s really just hitting a hot bit of metal with a hammer.’

Once the blade has been forged, you’re left with a piece of metal that is roughly the right shape and size, but needs cutting down to create the right profile. The metal is still extremely soft from the forging at this point, so the shape of the knife can literally be cut out – albeit with an industrial set of shears – and a Blenheim Forge logo can be stamped into the blade.

‘The surface of the blade up here won’t be touched from this point on,’ says Rich, pointing to the original iron cladding at the top of the blade. The original billet has, in effect, just been stretched out, creating an ultra-thin layer of Blue Paper steel in between two thin layers of iron cladding. That cladding is what you can see at the top of the blade near the spine.

After being forged at 1100ºC, the metal is still far too soft to make an effective knife. The process of heat treating – repeatedly heating and cooling the blade – is what hardens the steel again. Although every stage is important, the heat treatment stage has the most potential to completely ruin a knife, says James. ‘If you mistreat the steel when you're making a knife, it has a huge effect on the final outcome. You can do 90% of the work and then find out that the metal wasn't heat-treated properly, and the knife is completely useless.’ In the early days, the trio reckon nine out of ten knives ended up this way. Through trial and error, they’ve worked out a formula which gives them a much better success rate now, with only one or two knives in a batch ending up on the scrap heap.

From there, the knife goes onto the grinder, where Jon is busy with a recently treated batch of blades. ‘The dark area around the edge is the core – the Blue Paper,’ he explains. ‘You want to expose the core on both sides as evenly as possible, so you can sharpen the blade.’

‘The grinding isn’t always pleasant,’ he admits. ‘In January and February, the water gets freezing cold, so you start to lose feeling in your fingers after a while!’

After fifteen minutes on the grinder, the blade has a newborn edge – a dark wave of Aogami – followed by a multitude of smaller ripples, where layer upon layer of hyper-compressed metal is uncovered. When you think about it, this Japanese method of knife-making makes total sense – you take a minimal amount of high quality carbon steel, and use it exactly where you need it – at the edge – whilst cladding it with cheaper, more robust metal. It isn’t just beautiful – it’s smart, and extremely effective.

Most of these tasks are short and sharp, requiring intense focus to complete properly. A slip of concentration can result in significant damage to the blade or the bladesmith – as a result, the trio work on a rotation of sorts, meaning that no one is stuck outside freezing their knackers off for a whole day on the grindstone. Whilst Jon finishes off his batch, James is inside polishing some blades, tidying up the last few kinks ready for the handles to be fitted.

‘When we first started making knives it was a bit hardcore because we had other jobs,’ says James. ‘I used to work here making furniture, and Jon and I would come in on the weekends to make knives. When my boss decided to move out, it seemed a shame to let the workshop go, so we stayed – we figured we could pay the rent by selling knives.’

Making rent was about all the guys could do for a while, but it was worth it to stay – workshops like this aren’t exactly ten-a-penny in London, especially ones so central, and with an outdoor space for metalworking. The workshop itself is a craftsman’s dream, spacious and airy, with a huge south-facing window at the back that floods the space with sunlight in the afternoons. A new addition to the team, Dan, is busy fitting walnut handles to newly forged blades. ‘There are little jobs like sanding the handles, oiling the wood, packaging the knives – they’re quite mindless and relaxing, but they still have to be done nicely,’ he says. Music blares out of a boombox in the middle of the room – Rich is today’s selector, and the music is eclectic (and interspersed with YouTube adverts) but all very appropriate for working with power tools.

'There was a time when you wouldn’t have all the power tools we have,’ say Jon, reflecting on the way the team works now, ‘but even then, blacksmiths would still have a big forge, a big grindstone, and probably much more labour. Instead of a power hammer for example, you’d have loads of strikers – just people with hammers. It’s basically the same thing!’

The group resisted getting tools in the beginning, but soon realised that they couldn’t make a truly knife without really nice tools. ‘It still takes a lot of skill and practice,’ Jon continues. ‘Those grindstones for example, it takes a lot of time to learn how to use them well. We wouldn’t be able to produce the quality of knife that we do without them, regardless of how skilled we were as knife-makers.’

In that sense, you could argue that Blenheim Forge is producing some of the best knives ever seen – combining modern tools, ancient techniques and considerable skill to produce something very special. The trio are even starting to get some orders from Japanese retailers who want to stock them – as good a sign as any that they’re making world-class blades.

It’s five o’clock, and the guys down tools. Gone are the days when James and Jon would work well into the night – ‘we learnt pretty quickly that you can’t just drink coffee and make knives,’ says James. As we leave in search of a pub, a train rattles over the bridge into Peckham Rye station – thousands of people pass over the forge every single day, but only a few know the magic that is going on underneath their feet.