The Science Behind The Knife – Knifemaking Technical Information

A good knife is much more than a piece of sharpened steel.

Its performance is determined by the interaction between the steel itself, how that steel is processed and heat treated, the geometry of the blade and edge, the ergonomics of the handle and, most importantly, what the knife is intended to do.

My approach to knife making is strongly influenced by more than 55 years of experience in metallurgy and engineering at the MOD, auto and mining sectors.

I believe that understanding the material and the processes involved is just as important as the craftsmanship required to turn them into a finished knife.

One of the questions I am frequently asked is: “What is the best steel for a knife?”
The honest answer is that there isn’t one. Different applications demand different characteristics.
A culinary knife may benefit from a fine, stable edge and good corrosion resistance. A bushcraft knife may place greater emphasis on toughness and resistance to damage. A hunting knife may require a carefully considered balance between edge retention, toughness, corrosion resistance and ease of maintenance.

The properties I consider include:

• Hardness
• Toughness
• Wear resistance
• Corrosion resistance
• Edge retention
• Edge stability
• Ease of sharpening

Selecting the steel is therefore the beginning of the process rather than the end of it.

AEB-L Stainless Steel

• AEB-L is one of the steels I use for culinary knives.
• It was originally developed for razor blades, and its characteristics make it particularly interesting for fine cutting applications.
• AEB-L can be heat treated to produce a fine microstructure and a combination of hardness and toughness that makes it well suited to a keen culinary edge.
• It also offers the corrosion resistance that many cooks appreciate in a kitchen environment.
• For me, one of its attractions is that it demonstrates an important principle of knife making: A good knife steel does not have to be exotic to produce an excellent knife.
• The final performance depends upon how the material is treated and how the blade is designed and ground.
• However, AEB-L and its equivalents are not a one size fits all. 440B has better corrosion resistance and Niolox with it additions of Molybdeum, Vanadium and Niobium make it as good as you’re going to get in a non-powdet metallurgy steel. Then, powder metallurgy stainless steels are a quantum leap better. However, Powder Met steels are very, very expensive and very, very difficult to grind and finish, making knives in these super stainless steels extreemly expensive.

1095 & 15N20

I use mainly 1095 and 15N20 as the principal steels in much of my Damascus work. Sometimes I substitute 1080 or CS80 for the 1095 if 1095 is unavailable or if I’m creating special effects in the Damascus patterns.

1095

1095 is a high-carbon steel with a long history of use in blades and tools.
Its high carbon content allows it to develop high hardness when appropriately heat treated.

15N20

15N20 is another high-carbon steel, but with a significant addition of nickel.
That nickel is particularly useful in Damascus because it provides a strong visual contrast with the darker 1095 layers when the finished blade is etched.
The two steels are both good knife steels in their own right and therefore work particularly well together both from a practical and visual perspective.
However, Damascus performance should never be judged simply by looking at the names of the steels involved.
The construction, forging, thermal processing, heat treatment and final geometry all matter.

Damascus is a family of techniques rather than a single material with one fixed specification.
In my Damascus work, different steels are forged together into a billet and manipulated to create a layered structure.
The billet can then be drawn, cut, restacked, twisted or otherwise manipulated before being forged towards its final dimensions.
Grinding and etching reveal the contrast between the different steels and produce the characteristic pattern.
An interesting point here is that, individually, each steel will etch black in acid. However, when forged together there is an chemical-electrical interaction between the two steels that prevents the 15N20 from etching.

I make my own Damascus, including:

Ladder Damascus
Raindrop Damascus
Twist Damascus

I also make:

San Mai
Cu Mai
Ni Mai

Because each Damascus billet is individually made, the resulting pattern is unique to the particular blade.

Ladder Damascus is created by cutting slots into a plain layered billet in a controlled way to produce a repeating ladder-like pattern.
The exact appearance depends upon the construction of the billet and how it is subsequently manipulated, forged and ground.
The pattern therefore becomes part of the design of the finished blade rather than simply being applied as decoration.

Raindrop Damascus produces a series of rounded or oval forms within the layered structure.
The pattern is created through controlled shallow drilling of the billet before the final forging and grinding stages.
As with all handmade Damascus, the finished pattern will have its own individual character.

Twist Damascus is produced by twisting a layered billet before forging it into the required dimensions.
The twisting action changes the orientation of the layers and produces a flowing spiral pattern when the blade is subsequently ground and etched.
The final appearance can vary considerably according to the construction and manipulation of the billet.

“San Mai” is a translation from Japanese roughly meaning 3 layers. It is a generic term applied to knife construction where a decorative cladding is forge welded to either side of a high quality core. The Cu Mai and Ni Mai described below are my versions of San Mai.

Cu Mai is a laminated construction incorporating copper and steel cladding forged either side of a steel core.
Copper provides a very distinctive visual contrast and allows a different aesthetic from conventional high-carbon Damascus.
It is particularly interesting for bespoke and collector’s knives because the construction itself becomes an important part of the design.
As with any laminated blade, the quality of the finished product depends upon sound construction, appropriate processing and suitable heat treatment of the blade’s steel components.

Ni Mai is similar to Cu Mai but with pure Nickel replacing the copper.
The construction can produce a striking combination of a highly functional cutting core and contrasting material on the sides of the blade.
It provides another way of combining performance and visual character within a bespoke knife.

Is Damascus better than conventional steel?

Not necessarily.
This is something I believe is important to state clearly.
A beautifully patterned Damascus blade is not automatically a better cutting tool than a well-made mono-steel blade.
A good knife depends upon the complete combination of:

Steel + processing + heat treatment + geometry + edge + ergonomics

Damascus provides opportunities for craftsmanship, individuality and visual interest, as well as the potential to combine different materials.
But the pattern itself does not make a knife perform well.
Good metallurgy and good knife making still matter.

Heat Treatment

Turning Steel into a Working Blade

Heat treatment is one of the most important stages in making a knife.
The Steel’s properties are strongly influenced by its microstructure, and the microstructure can be changed through controlled thermal processing.
The broad stages involved in heat treating many blade steels include:

Normalising → Austenitising → Quenching → Tempering

The precise process depends upon the steel being treated. My 55+ years, mostly spent in a heat treatment environment, means I can tweak standard heat treatment procedures to get the very best out of every blade I make.

Normalising

Normalising is a critically important stage for any steel that has been forged. The forging process upsets the microstructure of the steel to a degree that it cannot be properly heat treated as per below. Normalising can be from 1 to 3 stages of therlal cycling designed to return the microstructrure to a state suitable for subsequent heat treating.

Austenitising

The steel is heated to an appropriate temperature so that the required metallurgical transformation from a soft to a hard state can occur.
The objective is to produce the appropriate austenitic condition before quenching.

Quenching

The steel is then cooled at a controlled rate which can be from cooling in still air to immersing in iced brine or anything in between.
For suitable steels and processes, this allows the formation of martensite, producing the high hardness required for a functional cutting edge.

Tempering

Freshly quenched steel can be extremely hard but also highly stressed and usually too brittle for practical use.
Tempering modifies the resulting microstructure and reduces internal stresses, allowing a more useful balance of hardness and toughness to be achieved.
The precise heat-treatment cycle depends upon the steel, the blade and the properties required.

It is tempting to think that the hardest blade must be the best blade. It isn’t.
A knife needs an appropriate balance between hardness and toughness.
Hardness is associated with resistance to deformation and wear.
Toughness is the ability to withstand damage and absorb energy without fracturing.
A very hard, relatively brittle edge may hold an edge extremely well under the right conditions but be less tolerant of abuse.
A tougher blade may sacrifice some wear resistance in return for greater resistance to damage.
Although these properties are related, they are not the same thing. Increasing hardness reduces toughness and vice versa.
The correct balance depends upon what the knife is expected to do.

Why Two Knives Made From the Same Steel Can Perform Differently

This is one of the most important principles in knife making.
Two blades can be made from exactly the same steel and still perform very differently.

Why?
Because the steel is only one component.
Differences in:

• Heat treatment
• Hardness
• Blade thickness
• Grind geometry
• Thickness behind the edge
• Edge angle
• Distal taper
• Surface finish
• Handle design
• Intended application

can all influence the performance of the finished knife.
This is why I don’t select steel in isolation. I consider the complete knife.

Blade Geometry

The shape of the blade matters

A knife cuts because of its edge, but the geometry leading to that edge has a major influence on how efficiently it cuts.
Important considerations include:

Blade thickness

Thicker blades can provide strength and stiffness but may create more resistance when passing through material.

Primary grind

The primary grind determines how the blade transitions from its full thickness towards the edge.

Thickness behind the edge

This is particularly important for culinary knives.

A blade can be made from excellent steel and still feel disappointing if there is excessive material immediately behind the cutting edge.

The edge needs to be appropriate for the intended use.

A very fine culinary edge and a hard-working outdoor knife have different requirements.

Distal taper

Reducing blade thickness towards the point can influence weight, balance and cutting behaviour.
The geometry therefore needs to be considered as a complete system rather than as a collection of individual measurements.

Culinary Knife Geometry

For a culinary knife, cutting efficiency and edge behaviour are particularly important.
The knife should move through food cleanly rather than relying on excessive force.
Blade thickness, grind, distal taper, edge geometry and balance all contribute to the experience of using the knife.
A knife designed for precise vegetable preparation may have very different requirements from one intended for heavier kitchenwork. A Sushi knife will need a complex convex grind, often with a 100% or 70/30% left or right handed bias.
This is one reason I prefer to discuss how a customer actually cooks and uses a knife before deciding upon the final specification.

Outdoor knives present a different set of requirements.
Toughness and edge stability become increasingly important where the knife may encounter harder materials or more demanding tasks.
The geometry therefore needs to reflect the intended use.
A knife designed primarily for fine carving does not necessarily need the same geometry as one intended for more robust outdoor work.
The best design is the one that is appropriate to the job.

Carbon Steel vs Stainless Steel

Neither is inherently “better”. They simply have different characteristics.

Stainless steel

The principal advantage is increased resistance to corrosion and staining, making stainless steels particularly convenient for many culinary applications.
As a general rule a stainless blade will stay sharper for longer than an identical carbon steel blade. This is because stainless steels contain a lot of chromium and chrome carbides are much harder than the iron carbides in carbon steel. However, stainless blades require more effort to re-sharpen which is one reason that carbon steels have the reputation of being easier to sharpen.

Carbon steel

Carbon steels can provide excellent cutting performance and can develop a distinctive patina with use.
They do, however, require greater care to prevent corrosion.
For someone who enjoys maintaining their knife, a carbon-steel blade can be extremely rewarding.
For someone who wants minimum maintenance, stainless steel may be the more appropriate choice.
The right answer depends upon the owner.

The Edge

Where steel and geometry finally meet

The edge is the working interface between the knife and whatever it is cutting.
Its performance depends upon both the steel and the geometry supporting it.
An extremely fine edge can provide superb cutting performance, but it also needs appropriate steel selection, heat treatment and careful use.
A more robust edge may sacrifice some initial cutting efficiency but provide greater resistance to damage.
There is therefore no simple “perfect” edge.
The appropriate edge is the one suited to the knife’s intended purpose.

A knife should not only cut well—it should feel right in the hand.
Handle shape, dimensions, balance, grip and surface finish all contribute to ergonomics.
I stabilise all woods for my handles “in house”.
For bespoke knives, these characteristics can be discussed with the customer rather than accepting a predetermined production design.
I can also incorporate a range of individual handle materials, including selected African gemstones on suitable commissions.

Having lived in South Africa for many years, I developed a particular appreciation for the country’s strong knife-making community, craftsmanship and natural materials.
I occasionally incorporate African gemstones into bespoke knife handles where the material is suitable for the application.
This creates an interesting connection between my years in South Africa and the knives I now make in Wiltshire.
For a collector, it can also give the knife an additional story beyond the blade itself.

Why I Make My Own Damascus

Making Damascus rather than simply buying a finished billet gives me greater control over the material and the design.
It allows me to decide how the billet is constructed and manipulated and how the resulting pattern will work with the shape of the finished knife.
There is also something inherently satisfying about taking separate pieces of steel and transforming them into a single blade with its own individual pattern.
Every billet has its own history, and every finished blade is slightly different.

Engineering Experience Meets Knife Making

My knife making is the result of two disciplines coming together.

More than 55 years working in metallurgy and engineering taught me to think about materials, processes, tolerances, failure modes and performance.

My years in South Africa introduced me to the practical craft of knife making and the community of makers who helped me develop my skills.

Today I combine those experiences in my Wiltshire workshop. I don’t believe that engineering and craftsmanship are opposing ideas.

Good craftsmanship benefits from understanding the material and

Good engineering benefits from understanding how the finished object will actually be used.

That is the approach I bring to every Clarke Knife.

A Knife Is A System

Ultimately, I don’t regard a knife as simply a piece of steel with a handle attached. It is a system in which every part has a role.

Material
↓
Processing
↓
Heat treatment
↓
Hardness & toughness
↓
Blade geometry
↓
Edge geometry
↓
Ergonomics & balance
↓
Intended use

Get those relationships right and the result can be a knife that is not only beautiful, but genuinely enjoyable to use.
That is what I aim for when I make a Clarke Knife.

Have A Question About Steel, Damascus Or Knife Performance?

If there is something about knife metallurgy, Damascus, blade geometry or materials that you would like to understand better, you might find some answers on my FAQ page if not, please get in touch.

I am always happy to discuss the technical considerations behind a bespoke knife and explain why I would recommend a particular material or design for your intended use.

The right knife starts with understanding the job it has to do.