We don't have any secrets at Tharwa Valley Forge and are very excited to be able to share all that we have learned about knives and bladesmithing. In addition to being the largest knife-making school in the world, we employ the largest number of full-time bladesmiths in Australia, so we've got a large base of knowledge to share with you.
Science, geography and warfare have influenced your kitchen utensils more than you might think.
The Sutton Hoo sword represents the state-of-the-art of sixth century sword making. For such an old sword the level of sophistication and complexity of its construction are surprising.
Like other swords of this era, it is a wrought iron sword with a resilient soft core and a sharp hard edge. The soft core consists of eight rods welded together that are themselves made from seven laminated layers twisted in alternating Z and S shapes. The sharp cutting edge is forge welded to the core and is a hard rod made from 180 layers of lamination.
Obviously, swords like this were very valuable. They took a significant amount of time and skill to manufacture and were passed down from generation to generation. Because the metallurgy of carbon steel is very stable, as long as you can keep it from rusting it and avoid abusing it with hard use, it will remain serviceable for hundreds of years. For example, the Kohoki Katana is an heirloom from 12th Century Japan that is still in remarkable condition.
Value, sentiment and social status weren't the only reason swords were passed down over generations. Early metallurgy meant the only way to guarantee the quality of a blade was to use it. Early middle age iron sources and smelting techniques were imprecise, and many blades had serious flaws that would only have become apparent after they'd seen use over time.
Accordingly, literature from a range of cultures cites "old" or "ancient" steel to be the best steel. This doesn't mean that the steel is necessarily older than other steel, rather that time has proven that it is of superior quality. Epics of the period such as the poem Beowulf make a big deal of "blood-hardened swords" that had seen use in battle. These swords were known to be free of defects because they hadn't failed despite repeated use in battle.
Bent and Broken Swords
At a microscopic level steel is a crystalline lattice of iron and carbon atoms. All steel has imperfections in this lattice, and these imperfections allow the propagation of microscopic cracks when the steel sees hard use. With repeated hard use these microscopic cracks accumulate, weakening the steel over time and eventually leading the steel to bend or break.
Good steel has relatively few defects, meaning microscopic cracks cannot propagate far, allowing more use before the accumulation of microscopic cracks leads to failure. Unfortunately for early medieval bladesmiths, they had no way of assessing which newly completed weapons were good in this way.
Defects in steel were the norm in early medieval steel and manifested as bending, chipping, and even breaking if a serious defect allowed a crack to propagate all the way through the steel. Blades that had seen repeated use over time were therefore free of major defects, and although they had accumulated a degree of fatigue through use, were valuable as examples of reliable high-quality steel.
The advent of better steel smelting techniques changed everything and the effects are visible even today - particularly in our kitchens.
Advances in Metallurgy
High quality steel made using a crucible process had been manufactured in Central and South Asia since about the 6th century BCE. This type of crucible steel was generally known in the West as "Wootz" steel and attained a kind of legendary status.
Although crucible steel processes had been used in Europe periodically since the 9th century CE, it wasn't until the high middle ages that they were re-discovered and began to see widespread use.
The production of large amounts of high-quality steel lead to the proliferation of vastly improved swords that cost substantially less to produce. This allowed armies to equip a greater number of combatants with edged weapons designed for users with limited training. This in turn drove the development and adoption of improved armour, which in turn produced evolutionary pressure on sword development. This ultimately lead to the evolution of general purpose swords that could perform a range of piercing and chopping tasks even when wielded by unskilled combatants.
Japan never experienced Europe's steel-smelting revolution, and traditional pattern-welding construction techniques persisted into the post-medieval era. The relative peace of the Tokugawa shogunate era meant that Japanese swords did not experience strong evolutionary pressures away from traditional designs or into the hands of unskilled wielders. Japanese swords remained expensive heirlooms that required knowledge and skill to wield effectively.
These fundamental differences created radically different approaches to blade design and use, both on the battlefield and in the kitchen.
Japanese weapons were single-edged and curved, so different parts of the blade had specific uses and was thus given a specific heat treatment. The specialised nature of these blades required their user to have a deep and fundamental understanding of their use.
European steel production techniques allowed for inexpensive multi-purpose weapons that were straight and double-edged. Users of European style blades required less skill and experience than users of Japanese style blades.
You can see this influence in the kitchen. The traditional set of Japanese kitchen knives is made up of the Yanagi ba, Deba, and Usuba, each with geometry that is specific to purpose:
|Yanagi-ba||Create cut surfaces that are smooth, shiny and even to maximize taste|
|Deba||Cleanly fillets and beheads fish without breaking on bone where other Japanese knives would due to their task specific edges|
|Usuba||Cuts through firm vegetables without cracking them, allowing the user to create smooth thin slices with exquisite flavour|
Compare this to Western kitchen knives, which are not as specialised. One Western knife can do the job of many different Japanese knives, but nowhere near as well. Western kitchen knives tend to have similar geometry regardless of task, with the size of the knife determining the purpose.
Blade Evolution Continues
The last 100 years has been a golden age for both Japanese and European kitchen knives. Bladesmiths have been riffing on elements of both cultures resulting in phenomenal advances for all cooks. The Western adoption of compound grinding has seen the development of chef knives with S and W grinds that produce cuts with an incredibly smooth surface and low friction.
Meanwhile, Japanese bladesmiths have applied their design thinking to western cuisine with superb results. The Gyuto (literally "beef-sword") is the Japanese enhancement of the Western professional chef's knife that has the utility of a German or French kitchen knife and the sensitivity and control of a Japanese knife. It can be used for mincing, slicing, and chopping vegetables, slicing meat, and disjointing large cuts.
Metallurgy is now at a stage of development where just about anybody can make a good knife given access to the right equipment and know-how. But some things never change: it still takes dedication and hard-work to make a truly great knife.
Everyone knows they need to rest meat after cooking so that the juices don't run-out when they cut it. So why do so many people tear their steak apart with serrated knives that leave the juices all over the plate instead of in their mouths?
The cutting action of serrated knives rips and shreds meat to create the cut. This produces a traumatised region of tissue with a very large surface area that allows a high rate of fluid loss out of the cut surface and onto your plate.
Steak knives with a straight edge create a far cleaner cut that has much lower surface porosity, resulting in fluid loss that is extremely limited compared to cuts created with serrated edges. They can also slice meat into much thinner portions, giving you that melt-in-the-mouth experience.
So why are serrated edges on steak knives in the first place? A combination of convenience and 1970's BBQ techniques.
If you were around in the 1970's then you'll no doubt recall that most people enjoyed their steak somewhere between "well done" and "car tire." Steak of this consistency necessitated the use of serious quantities of tomato sauce and cutlery that could see double duty pruning tree branches. Fortunately, society today is more conscious about combining quality ingredients with the correct cooking techniques; unfortunately we're still playing catch-up when it comes to cutlery.
A plate is about the worst cutting surface anyone could dream up - it's hard and will turn the edges on sharp knives rather quickly. Serrated edges also suffer from turned edges, but only on the 'hills' of the edge; the 'valleys' of the serrated edge never touch the plate and these are the parts of the edge that perform the bulk of the cutting work.
If you use steak knives with a straight edge you are going to find yourself sharpening them on occasion. This isn't as onerous as some might think: it only takes a few passes on a honing rod after each use to keep an edge well maintained. This means that the practical difference between serrated knives and straight edge steak knives is a little know-how and a few seconds of maintenance after each use.
Serrated steak knives are similar to stainless steel in that they trade quality and performance for convenience. This has caused many people to forget how great carbon steel knives are, much the same as cheap serrated steak knives have lead us to forget that there is a better way to eat steak. It seems such a shame that people spend so much time and effort cooking wonderful cuts of meat only to rob themselves of the full-flavor by using sub-par cutlery.
Asides from their highly specialised cutting geometry, Japanese kitchen knives are also notable for their distinctive handles. Home cooks frequently overlook the mechanics and ergonomics of knife handles, neglecting an element that factors into the performance of a knife as much as the shape, size, and grind of the blade.
Almost all professionals prefer carbon steel blades because they have the sharpest edges, stay sharp for far longer, and are easier to sharpen than stainless steel blades. With a modicum of knowledge and a minimal amount of care you too can enjoy the superior performance of carbon steel blades whilst getting a literal lifetime of service out of your knives.
I was making a large kitchen knife for a client, when I realised that it wasn't going to fit in my knife vices to shape the handle. So I made a new holder that bolts onto the existing bracket just for this one. It is a monster - 75 x 25 x 350mm. Enough for the biggest of blades. It needed three screws to squeeze the blade tight.
A nice feature of the Knife Vice Mark II design is you can have different sized clamps that fits different blade. Easy to swap in and out as required.
When hardening blades, especially large ones, warpage can sometimes occur. The choice of steel can minimise the risk, as can a good normalising cycle, but sometimes it just happens.There are a number of different ways to try and fix the bend, not all of them are guarenteed.
One gentle way is to use a Japanese straightening stick or "Magebo". I found this in Murray Carter's excellent book "Bladesmithing with Murray Carter". It is made with a large piece of hardwood, by cutting a slot or to (just thicker than the blade thickness) and making a handle. The bent blade is first tempered, then the back softened. This is to reduce the risk of breaking. The blade is then placed in the slot, where the bend is, and some gentle pressure applied to torque it straight. Gently does it.
It possiby could be used straight after quenching when still hot, I'll have to try it. I dont normally expect my blades to warp, but should have the Magebo hanging up near when I heat treat for emergencies.
I asked John Price from Radiusmaster what he recommends for belt grits in grinding a knife. His tip was to use a sequence of belt grits 60, 150, A45 then A6 to take it to almost a hand rubbed finish level. This is the smallest number of belt changes he recommends.
A good quality 60 will remove stock without putting too many scratches in. The 150 will clean out the 60 scratches before leaving an even finish. The A45 and A6 Trizac belts put the final touches on. The blade can be quickly hand sanded with 500 wet and dry for a satin finish, or higher grits before being buffed for a mirror polish.