Jay Fisher - Fine Custom Knives

What is O1?
(Specifically Tungsten-Vanadium O1)

A tool steel. Tool steels are primarily used for making tools used in manufacturing and trades for the working and forming of metals, woods, plastics, and other industrial materials. Tool steels must withstand specific loads concentrated at exposed areas, and withstand severe changes in temperature, abrasives, shocks, and loads. O1 is composed of these major alloy elements (I don't list the minor elements since they don't play a major role) :

• Carbon: 0.90% This increases hardenability and wear resistance, but decreases toughness in higher amounts.
• Manganese: 1.20% This is added to reduce brittleness and improve forgeability, hardenability, and reducing deformation.
• Silicon: 0.20% This is a deoxidizer and improves hot-forming properties.
• Chromium: 0.50% This improves hardenability, high wear resistance, and toughness.
• Vanadium: 0.20% Refines the carbide structure, forms a hard carbide that increases wear resistance
• Tungsten: 0.50% Improves hot hardness (resistance to elevated temperatures) and forms hard, abrasion resistant carbides

These basic elements (along with iron) are a simple combination that works well together, and has for decades.

Non-standard O1?

Okay, you can't blame him for trying; everybody wants to spank the knifemaker... or get an education!

If you are up on your metallurgy, you'll note that what I list above is NOT the standard O1 alloy set. This is because I don't use the standard O1 alloy, because it does not contain tungsten or vanadium. So, this page is not about standard O1, it's about the tungsten-vanadium O1 which is also classified as type Low Manganese O1. I found years ago that the performance of this type of O1 is substantially improved over the standard O1 alloy, because of the tungsten carbides and vanadium carbides formed after processing of this steel. The drawback is that it is much harder to polish, as the little carbide particles skid and create tiny waves on the surface when sanding in the finer grits and during polishing. But no worry; your knifemaker has figured out the formula for accomplishing magnificent polishes with this steel. Other makers may shy away from the tungsten-vanadium bearing alloy, because they simply can't get a good finish. That's not stopping me; I love it!

For more information, link to my Heat Treating and Cryogenic Treatment of Knife Blades page.

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O1: Good Wear Resistance in a Low Alloy

AISI (the American Iron and Steel Institute) has classified O1 as a Cold Work Tool Steel. This means that it has a relatively low percentage of alloy elements, particularly when compared to some of the stainless steels I use for my knives. It's also touted as a less expensive tool steel, but if a knifemaker chooses the tungsten-vanadium version ( I do) it is not inexpensive. In fact, this alloy set is more expensive than W1, A2, and other low alloy steels as well as being more expensive than all standard carbon steels and all typical (non-vanadium/tungsten bearing) O1.

O1 has a good depth of hardness, and it's easily machined. Though it may be used for power operated machine tools and dies, its life is short lived in those applications, and there are much better choices for these extreme (high speed, high pressure) uses. Knowing this, hand-operated tools made of O1 are a good fit, so taps and dies, reamers, broaches, blanking dies, hand tools, chucks, rolling dies, bushings, and plastic molding dies are well suited to O1.

O1 has good wear resistance. In knives, it has better wear resistance than all standard carbon steels, including the chromium bearing types like 5160. This is the difference in performance between what is classified as a standard carbon steel, and a tool steel, and O1 is a true and proven tool steel.

O1 is an old steel; it's been around a long time. When I write "long time," please understand that alloy steels (at least the ones that are recorded, repeated, and sold in raw form or products) have only been around since the latter part of the 19th century. This time was the great industrial growth period, from which all alloy steels have sprouted, and will continue to develop. O1 was an early player in the industrial revolution. It's interesting to note that Mushet steel (1868) is considered the ancestor of all modern tool steel, and was high in carbon, tungsten, and manganese, all critical components in today's O1.

Here's a chart comparing O1 cold work tool steel (tungsten/vanadium type) to more commonly used steels typically found in hand-forged knives:

There are some important comparisons in the chart. The first is the alloy type. 1095 and 5160 are commonly used in hand-forged knives because they are inexpensive, forgiving to work with, and easily hand-forged into a knife. Note that they are both standard carbon steels, and both make a dependable, useable knife.

1095 gets its performance from the high carbon content. It's used industrially to make farm implements, springs, and even music wire. Some of the farm implements using 1095 are scraper blades, discs, spring tooth harrows, cultivator shovels, plow shares, binder sections, twine holders, and knotter discs. You can see that 1095 is a readily available and common steel, so it's easy to acquire 1095 with little expense.

5160 has much less carbon, but derives its good wear characteristics from the addition of a small amount of chromium. Here's a topic on chromium in steel alloys on my Blades page. This small amount of chromium improves hardenability and wear resistance, but is not enough to improve corrosion resistance. Where this steel excels in industrial uses is in case hardening. This steel can be processed to achieve a very hard and wear resistance surface and a tough interior, which is why it is used for gears, pinions, piston pins, ball studs, crankshafts, universal joints, and other bearing surfaces. In the application of a knife blade, case hardening is not applicable, because of the very thin cross sectional geometry of the blade, and the constant exposing of the blade core by sharpening. If differential hardening or tempering is used to create a temper line or hamon, this means that the cutting edge itself is brittle, while the spine is more flexible. This is a sad limitation of this steel, as a thin cross sectional area of blade, left hard and brittle, can chip more easily than the tempered spine. Alloy 5160 also a leaf spring steel, so is easy to acquire and relatively inexpensive. Some of my earliest knives were made of leaf springs, and it is very simple and easy to fabricate a blade from.

O1 is a true tool steel, not a standard carbon steel. It derives its performance from a variety of elements in the alloy. It has high carbon, which improves hardness and hardenability overall as well as improving wear resistance. It has a higher level of manganese, which improves its overall forgeability, and hardenability while adding dimensional stability. It has significant chromium to increase hardenability and wear resistance, but not enough to increase corrosion resistance. It has vanadium and tungsten that help in forming incredibly hard and wear resistant particles of vanadium carbide and tungsten carbide. It is this particular set of alloy elements that gives O1 superior performance over the two other alloys listed, and many other alloys as well.

It's important to remember that O1 is a true tool steel. Tool steels are a special classification of steels, and they are designed specifically to make tools to cut, press, form and work other materials, including metal, woods, and plastics. The previous two listed alloy types were not specifically designed to be tools, and you can see that from the applications I listed that there are much more economical applications for these steels. I did not make these up, they are detailed specifically in the Machinery's Handbook®, the standard reference for machinists and engineers. While O1 is specifically designed to be a tool, it doesn't preclude the standard steels from being used for some less demanding uses, and standard carbon steels are often used in these applications, such as hammers, files, wood chisels, and mining bits.

The reason I compared these three steels is because they are somewhat similar in most knifemakers' toolkits, and people often think the three are interchangeable. They are not. Of the three, if you are commissioning a knife to be built, O1 is far superior to these and many other steels in this application.

O1 is a very good tool and knife steel.

What about O2?

O2 is similar to O1, with some distinct differences that should be mentioned. The main difference in O2 is that it contains significantly more manganese. The Machinists' Guide details that "Manganese is the dominant alloying element in in this type of of oil hardening tool steel..." The reason for adding more manganese is to increase the forgeability, workability, decrease the possibility of deformation, and to make the steel easier to machine. This is great if your item is difficult to machine, such as a complex forming die or unusually shaped mechanical part. The increase of manganese helps in making the machining and forming job easier. This is not particularly relevant to the knife owner and user, but only to the maker.

Manganese has some additional properties. It increases the depth of hardening, but this is not particularly relevant in knife blades since they are so thin to begin with. The depth of hardening would be of greater concern if an object to be made has thick cross-sectional areas (think of a heavy, two-inch thick forming die) where the depth of hardening needs to be deep within the metal object's core. So some sources simply state that in this way, manganese improves "hardenability." Please note that chromium (found in O1) also adds to the depth of hardening, and chromium adds several other significant factors as well. Chromium carbides contribute tremendously to the wear resistance, important in knife blades. O2 has no chromium.

There are drawbacks to this that are worth noting. Increasing manganese substantially in higher alloy steels is detrimental, and increasing the amount of manganese has a "marked effect in increasing brittleness and the danger of cracking on quenching" (from the ASM Handbook of Machining). So the manganese amount has a limit, particularly when high amounts of other alloying elements are used.

It's worth noting that adding percentages of one element means a reduction in others, simply by volume. O2 has a reduced volume of some critical components that are advantageous to knife blades specifically. O2 does not typically contain tungsten, vanadium, or chromium, and this is key. Tungsten forms incredibly wear resistant tungsten carbides, and improves the hot hardness (not extremely important in knife blades since they are not usually heated in use!). Chromium improves hardenability (much like manganese), and also provides additional wear resistance and toughness. O2 typically has no vanadium, and some O1 does not either, but the O1 I use does have vanadium and this imparts tremendous wear resistance, helps to refine the carbide structure, and improves the forgeability of the steel.

So why use O2? The applications for O2 are somewhat limited, and this is why you don't often see O2 sold through United States outlets. There are steels that are much more shock resistant, and steels that are more wear resistant. Additionally, we have advanced machining technology and abrasives that allow workability of some of the hardest, toughest, and strongest alloys, particularly in simple knife blade construction. This means that workability is not as critical a factor in knife blade machining. Where one would consider the application of O2 would be thick and complex shapes of machined metal, where depth of hardening is important, and workability of the metal is more important than final wear resistance.

Simply put, O1 is a better choice for knife blades, particularly where wear resistance is key. High tungsten, high vanadium O1 is a better steel for knife blades than O2.

For more information on steel alloys, transformation, and applications, link to my Heat Treating and Cryogenic Treatment of Knife Blades page.

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It's about the blue

Because O1 has very little chromium, it is not corrosion resistant in any way. Bare, untreated O1 will corrode and rust at the very first opportunity, ultimately pitting, scaling, and if left wet, rusting and dissolving! It is clearly a steel that must be maintained, even when treated.

So why do I use it? After all, the stainless alloys have higher wear performance, some have higher toughness, and all can be exposed to a wet atmosphere without worry. It's about the blue.

Bluing is a very old process, and you might wonder why it's called blue. In early times, oxidation of steel was called "browning" due to the color achieved on the surface. So when chemistry and process was developed further to produce a deep blue-black surface color, the treatment was called "bluing steel." Also, some nitrate salt treatments actually result in a beautiful cobalt blue color.

O1 can be blued. Because of the low chromium content, this steel readily responds to bluing in several different types of bluing processes and operations. While there are special chemical baths to blue some high chromium stainless steels, they are unpredictable and finicky, so I don't ordinarily hot blue stainless. I do have a black oxide surface treatment for stainless steel, but it is not as chemically deep as hot bluing, and it is more of a wispy slate color, not jet black. I use it on my "Shadow" line of counterterrorism knives.

When a client request a very black blade, O1 is king. Mirror polished and hot blued O1 is jet, glassy, slick, deep black, and no other material looks like it or performs like it on a knife blade. Consequently, all of my O1 knives are blued, no matter if the finish is flat, satin, media blasted, or mirror. I can't remember ever having made an O1 blade that I have not professionally hot blued.

Bluing is a process of controlled oxidation. Early bluing was done by applying acidic compounds, letting them rust and corrode the surface, brushing or burnishing the surface, applying more compounds, allowing them to react with the surface, followed by more brushing and burnishing, and ultimately sealing with oils, fats, or waxes. Early steel workers found that after a while, the corrosion seemed to stop, while the surface achieved a darkened, patinaed appearance, and further corrosion was inhibited. Through experimentation and development, specialized salt baths were created to impart specific appearances in the surface, while inhibiting further corrosion. This is the history of bluing. When you see a black firearm, know that (unless it's coated with a bake-on spray), it's hot-blued. If you are aware of how difficult it is to get a blued firearm to rust, you're familiar with the corrosion inhibition of bluing in a classic form.

Most of my blued knives are hot blued with a sodium-based salt solution, here in my studio. The blades are finished to their completed stage, and no fittings or handles are attached. The bluing baths are very particular to any contamination, and organics and other metals will ruin a bath at the slightest exposure. The blades are degreased and chemically cleaned, and cleaned, and cleaned again, to achieve the most sterile surface. Then they are immersed in the hot bath for twice the time most firearms are blued. This produces a black, controlled oxidation deep into the steel surface, and then the surface has to cure through another process set and time. This results in a surface that inhibits further oxidation and corrosion, and, of course, colors the blade black.

I also have a nitrate-based solution, which produces a peacock blue of cobalt, vermillion, straw, and even reddish color. I use it infrequently and for art knives because this bluing is fairly shallow, and requires a higher level of care and attention. It's done mostly for appearance, and less so for corrosion inhibition.

Note that I define bluing as corrosion inhibition not corrosion prevention. Even blued steel must be cared for with greater attention than stainless steels. Regular waxing and keeping the blade dry with access to dry air is important to prevent corrosion. Bluing is only an inhibition, not a preventative.

If blued blades require more attention, why do I use blued O1? It's about the blue.

In combat knives, blued O1 is requested because it's not only non-glare, but it doesn't interfere with sighting and reflection, and is harder to see both day and night. It also contrasts machine engraving very well, no matter whether it's mirror, satin, or flat finished. I do not recommend it for damp or marine environments, but in the deserts, my blued combat and tactical knives have performed very well. The guys that use these understand the limitations and are mindful of the corrosion prevention care required.

In art and collectors' knives, blued O1 is stunning. Nothing looks like it; it is a magnificent finish that will stand the test of time for generations with minor care. Some knives just look better in a clear, glassy black, and blued O1 can deliver. You can see this from the photos on this very page.

Note that there are two ways to photograph blued steel, one is with a white reflector, which can show the grind lines well, but without a reflector actually shows the density of the blackness of this finish.

When you want a black blade, nothing beats hot-blued O1. Nothing.

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Why not just paint or coat the blade?

I detail this on my Blades page (at this bookmark), and here's the reason: For the same reason that you don't paint a ladder, I do not coat blades, because that would hide any potential flaws, imperfections, or cracks, and any coating would eventually chip and peel. Coatings also have the potential to accelerate corrosion, because moisture, corrosive fluids, and debris can be trapped between the coating and the blade, and if the blade cannot breathe, dry out, and be cleaned, it will corrode. All fine tool steels (even high chromium stainless tool steels) can rust if stored in an enclosed environment (including the sheath) because there is no truly corrosion proof tool steel. Eventually, all coatings will become nicked or scratched or, at the very least, be exposed to an opening at the cutting edge. Coatings are typically the sign of a cheap factory knife, as it is a very fast and inexpensive way to finish the blade. Spray it, maybe bake it, and out the door it goes. I talk about that more on my FAQ page.

No matter what you read about coatings, how they are applied in a plasma stream, how they "improve lubricity," "prevent corrosion," or even "maintain sharpness," don't be taken in by this bunk. This is how knife makers and manufacturers avoid the arduous process of finishing their blades. They even have plastic sheet dye-sublimated wraps they're using on guns, vehicles, and the signage industry to "shrink wrap" knives. Anybody who knows dye sublimation is familiar with this process; look it up. This is a ridiculous, cheap, and horrible way to treat any fine knife. It's of advantage to the maker or manufacturer, not to the owner, as, sooner or later, these weak surface treatments will wear, tear, scratch, bubble, discolor, or even react with moisture, exposure, or a simple household cleaner to scar, melt, or deface the surface. Then the gimmicky coating is gone, or worse, holds moisture against the steel, leading to corrosion and destruction of the steel underneath.

If you need absolute high corrosion resistance, go with a stainless steel; it has corrosion resistance throughout. If you want a black blade, bluing reacts with the very surface of the steel; it is not a coating; it is the steel itself, and it won't chip, fade, peel, tear, or degrade over time.

If you want a tiger orange and lime green striped blade, well, then, you don't deserve a fine handmade knife anyway and you need to go away now. Quickly.

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What about the newer alloys?

Like 440C, ATS-34, and D2, O1 has been around a while. It's not a new, exciting, or proprietary steel, it's not a gimmick, not a flash in the pan. It's been around a while strictly because it is a very good steel; it has staying power. Because it is not new and exciting, O1 is not as often considered as some of the newer alloys.

Are there other good alloys? Of course there are, and some of them have marked advantages over O1. You may be surprised to hear that at the time of this writing, I use over a dozen different steels, and every one of them has certain advantages and certain (and sometimes defeating) limitations. Take the CPM steels, made by the crucible particle technology process. They are great steels; they are very expensive, and each one has its own attributes. CPM154CM is a beautiful steel, but when compared to O1, is much more expensive and limited in available sizes. CPMS35VN is tougher, but it can't be mirror polished, is very expensive, and limited in available sizes. You won't see this on their data sheets. By the way, don't always trust manufacturer's data sheets, Crucible Steel reps have told me face to face that there are "misprints" on these sheets. One such misprint is claiming that CPMS35VN can be mirror polished, when it can not be mirror polished due to the high vanadium carbides that are present after heat treating. Whoops! Okay, it's just a misprint. So if you can't entirely trust a manufacturer's data sheet, what can you trust? Who you should be able to trust is someone who has had decades of using many steel types for many knives; they are the guys with the know-how. More on that below.

Another example of presenting newer steels as superior can be found in what is not said. Many of these newer alloys have totally ignored finishing as a benefit. Finishing is the ability for a knife blade to be polished to a high, even mirror luster. This is critical in art pieces and investment grade knives, and also critical to keep the highest corrosion resistance possible. A rough blade corrodes easier, simply because of increased surface area. More on that topic here.

The most conspicuous and determinant factor in using any of the modern stainless steel alloys over O1 is that none of them can be predictably, easily, and regularly blued. 440C, ATS-34, D2, CPMS30V, CPMS90V, CPM154CM, CPMS35VN, Stainless Damascus, N360, and any of the steels containing more than a few percent of chromium can not be blued, at least not in this shop or any other custom knife shop I know of.

There simply is no ultimate steel for knife blades, no superior, magnificent, ultimate blade material. Each choice of steel for a knife blade is a decision of balance of many properties.

Knife buyers are just like everybody else; they can be swayed towards a particular knife buying decision based on advertising. Who wouldn't want the newest truck, the newest tool, the newest snack, or the newest knife? How do you make a knife, a tool that has existed for longer than any other tool in the history of man sound and seem new? Sure, people need knives, they use knives, and they collect knives. What could be more appealing than the newest, most exotic, most astounding performing steel made today? Why, even I would want to buy that! One problem though: it doesn't exist. See the next topic.

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Why do they claim their steel is superior and how can I find the truth?

There simply is no ultimate steel for knife blades: no superior, magnificent, ultimate blade material. Please understand this: If there were a steel superior to all other exotic metals, all others would be cast aside, no longer made at any foundry, and they would be sentenced to the ashbin of obsolescence. Every steel has its pros and cons, its advantages and disadvantages. So advertisers need to make something sound new and better (even if it is cheaper and worse), so they claim a new steel, a better steel, a rarer steel, a superior steel is used in their product. Isn't it funny that they never claim new or superior handles, bolsters, or sheaths, only the blade steel! That's because they know that you, as a consumer, have limitations that prevent you from knowing the truth. How does this happen?

• They know that you will not have the steel tested by a certified metallurgist to determine exactly what the steel is.
• They know that you will not use the knife in such a way as to notice any difference in any performance from earlier steels.
• They know that there is no real testing of knife blade steel performance, only subjective comparisons based on vague properties that are not scientifically defined.
• They know that if you are unsatisfied, they amount you pay is either not enough for you to care about, is not too much for them to refund, or that you will be satisfied with a replacement of the same item.
• They know that you are influenced, hoodwinked, and taken in by advertising hype consisting of unsubstantiated claims.
• They know that there is no official, law enforcing, or sanctioned authority that will police their lies, claims, and inflated hype to make them tell the truth in their advertising.
• They think you are too stupid, ignorant, or careless to bother to research the topics presented by proven masters and highly experienced professionals in this field, and will simply go with the herd.
• They know you, who are reading this website, are not their customers.

Okay, so is most of what you read about knife blade performance hype? It really depends on who is presenting it, and this is very important. If you are a knife client, buyer, or user, there is a simple way to know whether your knifemaker, knife factory, and knife supplier is selling the hype or knows what he is talking about. Look at his knives!

• Look at the website; if there isn't a substantial web presence, they are not modern or advanced makers tuned to make and respond to modern knife use, design, or appeal. Their website demonstrates their participation, or lack thereof, in the professional knifemaking field. Look for information, lots of it. There simply is no reason a knifemaker or (worse) a knife manufacturer will not take the time to offer every available piece of information about the product they sell. If I, as an individual knifemaker can do it, certainly a large corporation with dozens or hundreds of employees can too! If it's a single knifemaker you intend to buy from, know that how he "wears" his website demonstrates how he treats his clients, because this is the service aspect of our field. More on service at this bookmark.
• Look at his testimonials. Are they realistic, are they plentiful? Do they seem like they are all made by one writer, or do the individual testimonials have their own voice?
• Look who he makes for. This should be clearly presented, with plenty of references, testimonials, and types of knife in his particular field.
• Look at his history. A new maker is not an experienced maker. There is no shortcut, no fast track to knifemaking skill. There is no cultural claim to fine knives (like is so often seen in Japanese style sites and products). The history of the maker should be well established and clearly defined without hype.
• Overall and most importantly: LOOK AT THE KNIVES! Do they look finely made, are the grinds crisp and uniform, are the finishes complete and precise? Do they have an excellent and precise fit? Do they even offer large, clear, and plentiful photos that you can see the fit at all, or are they just small, dinky "profile" photos? Have they painted the blade? Are there three ridiculous rivets securing the handle to the tang? Is the tang tapered for balance? Are the blades ground to their purpose, are there a large variety of styles, patterns, and designs to choose from, or are they just 4" drop points? Are the handle materials wide-ranging and exotic, as well as domestic? Are there fittings on the knife (bolsters)? Are there good sheaths? Good stands, good cases? Or is the maker or manufacturer just making a simple, plain, boring knife, and then hyping the steel type in hopes you'll buy?
• Probably most important: does the maker make real combat knives? Why do I mention this? This is included because real combat knives are frequently the most durable, most well-made, most challenging, and most important endorsements of the maker's experience. I don't mean knives that are stylistically tactical, I mean real combat knives made for and used by professionals in the field of war, counterterrorism, or law enforcement. While many makers and manufacturers claim to be making these knives, their reputation, their illustration and their participation in this field is less tangible and more inferred. How do you know the difference between a maker or manufacturer who actually makes real combat knives and the company that just makes the claim? Hold on to your hat: it's the sheath. If a maker or company is making an actual combat knife, the sheath is just as important as the knife, and made just as durable, with specific and various options, with real mounting and interfacing hardware to work with the professional's gear. How do I know this? Because this is how every knife makes it into battle: in a sheath. So don't forget to look over what is (or what is not) offered in this critical part of the knife package; it will tell you a lot!

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Why don't you see more blued O1 blades?

O1 has a long history of performance; it's a great steel to work with, a great steel to build knives with, and it has good wear resistance, high toughness, and dependable sharpness while being easier to sharpen than many of the newer alloys. It's nothing new, it has a proven place in the machine tool trades, and performs better than all of the plain carbon steels an many of the tool steels. So why don't you see more blued O1 blades in fine handmade custom knives?

• It's not a new steel, therefore does not gain pop attention.
• It's difficult to finish, requiring a specific regime of steps and thorough attention to particular abrasive quality to properly mirror finish, particularly the tungsten-vanadium version I use.
• While it can be hand-forged, if a blued finish is desired, it will reveal any inaccuracies, inclusions, irregularities, or stressed areas of welds in the finish.
• It is difficult to blue. The temperatures, the bath consistency, the pre-treatment and post treatment add many steps and expense to the knife project, and may have to be repeated if any errors are made.
• Most shops do not have hot bluing facilities and equipment, and most knifemakers do not know how to blue.
• The post finishing of the knife after bluing is a meticulous and arduous affair. This is because one slip, one touch on the blued blade or any area of the knife that has been hot blued will ruin the whole knife, requiring reworking down to the bare, un-blued blade to start over.
• Most knife makers and manufacturers do not care about the finish that much. That's why most knives are only satin finished, sanded, or coated, because it represents a huge savings on the knife for them, which is not of any advantage to the knife owner.
• Because of the steps, materials, expendables, time and equipment involved in professional hot bluing, the blued blade can be more expensive than a non-blued blade. 

Bluing by a gunsmith shop:  It might be tempting to have a carbon steel knife (including tungsten-vanadium O1) blued by a local gunsmith shop. After all, if they are a professional repair shop, they should have the bluing tanks, cleaning tanks, solvents, post-treatment chemistry and other supplies and expertise to be able to blue your knife blade.

Most shops won't accept knives to blue, and they have good reason. Knife steel is not gun steel. Knife blades will already be hardened and tempered by the time they are ready to blue, and the hardness of the steel will change the requirements of the bluing bath. I won't go into details, but the gunsmith will have a set of process instructions that will have to be adjusted, fiddled with, tweaked and tuned to produce a specific and acceptable blue on a knife blade. It may take many trials and errors and corrections to achieve this, and every knife blade is different, for, if nothing else, slight variations in hardness. More so, the alloy content can radically change the bluing process steps and treatments. The gunsmith, not normally bluing high alloy hardened steel, will (and should) charge a lot for figuring out how to blue any particular knife. When he's done all this, and adjusted his baths, chemistry, and process steps, and has achieved an acceptable blue, he'll have to change everything back so he can perform his regular bluing!

Another worry is contamination. Hot bluing baths are very finicky, and the slightest contamination of polishing compound, abrasives, chemical cleaners, copper traces, aluminum, or brass even in the tiniest amount can kill a bluing bath dead. What happens is the contamination renders the bath useless, and the chemistry has to be replaced. The gunsmith can deal with his own prep, materials, and cleanliness, but to have a knifemaker hand him a blade of unknown exposure is a gamble. This gamble may mean the gunsmith has to replace his entire bath because of a bit of polish embedded in a milled hole in the handle that has a trace of copper or aluminum from using the abrasives or polish on those metals previously in the knifemaker's shop.

It's just too iffy, and it's easy to see why gunsmiths typically turn down knifemakers for hot bluing projects.

If that's the case, how do makers black-blue knives like pattern-welded damascus? Cold blue, that's how.

Cold blues are chemicals that darken the blade using selenium dioxide. The surface is cleaned and the chemical is applied with a cotton swab. The reaction is very fast, then the chemical is rinsed off, and dried. Cold blue is typically used for touch-up of wear areas, but it has only marginal resistance to being rubbed off. When a knife blade is cold blued, if it's a monolithic blade uniform finish, cold blue looks horrible: distinctly blotchy, irregular, weak, gray, and sometimes with a weird greenish-gray pallor. While it can be used to touch up a tang or wear area with good results, it's an adjunct, not a primary bluing process. In damascus knives, you usually can't see the blotchy appearance, as the blued areas are small between other, shiny or bright layers of the welds. It's important to use a high quality professional cold blue as well, as the off-the-shelf brands are quite watered down and weak and ineffective. Good cold blue is expensive. The most important limiting factor is that the cold blue is just a surface treatment, with very little penetration or longevity.

Hot bluing is expensive, difficult to achieve with attractive, regular results, and is best achieved by the same maker/shop/studio that creates and finishes the blade.

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Field Use

A lot of inquiries are about the durability of blued blades in field use. Will the blue stay, will it resist  scratching, will it resist corrosion, will it last?

It is entirely dependent on the level of care of the knife, and the exposure of use, just like any knife. If a knife owner is careful of his equipment, keeps it reasonably dry, does not store it in the sheath, and waxes it periodically, his blued steel knife can maintain its finish for many years in the field.

All knives in use can become scratched, and blued blades are no different. The scratches can not be abraded out, however, but then, I've never been asked to polish any used blade because marks on the steel acquired during use are expected. The patina and surface condition and appearance are a character of the knife and its journeys, and attest to the action it has seen and how it is depended upon. Consequently, I have made many knives that are hot blued and used by combat, rescue, and survival professionals, and they have had no complaints about the finish and the performance of O1.

One military client was digging with his blade in the sand in Iraq (I know, he apologized to me for using the knife as a shovel). He jammed the point deep into the soil and it speared a piece of vehicle armor plate... and stuck there! O1 is a great performer.

Other military clients are sold on hot-blued O1 and order sets of the steel/finish for all their tactical needs. The most powerful factor here is that the blade can be made black, flat black, without some cheap coating or spray, and these guys require non-glare, non-reflective, non-gray or steel-colored metals. Hot-blued O1 can deliver.

There are people in this field who simply mimic what they have heard. I've seen this for decades in this career field. This site and the book I'm writing are my attempt to clarify what has been misrepresented as fact by the uneducated or inexperienced.

Thankfully, I have many, many dedicated clients who do their own testing and use in the field, and these are actual trials of these critical tools in combat, rescues, working, and use. They swear by this steel, and often go on to buy more. They have real skin in the game, their own money, and this speaks more than any other type of evaluation. They have given me the freedom and resources to continue this wonderful journey, and I am eternally grateful for their business, dedication, and support!

Please look over the Paraeagle made for a United States Air Force Pararescueman, after he carried and used this blued steel knife for over ten years. Take a good look, this is the real thing after many missions.

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O1 is a Substantial Player

O1 has been around a while, and will continue to be a top choice in knife performance, particularly when a dark, black, or professionally blued blade is required or requested. It has some very distinctive traits: high toughness, high polish potential (in the hands of a skilled maker), and a high alloy version that has increased wear resistance.  The capabilities of finish are not  matched by other knife blade steels. This, coupled with a good array of available sizes and thicknesses, moderate pricing, and the steel's beautiful and flaw-free uniformity will make certain that this steel will always be valued by combat and working knife professionals and high art collectors, particularly when bluing is desired.

It will continue to be a top performer in its niche, and a regular in my knife studio.

For more information, link to my Heat Treating and Cryogenic Treatment of Knife Blades page.

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