Dulling Thoughts
Posted on | October 17, 2010 | 1 Comment
Print This Post
There’s a common belief that you can keep a knife sharp for a year or more by using a rod hone aka “knife steel.” WRONG-O!
All knives get dull. There’s only so much you can do with a steel. This isn’t just about my standards of sharpness, but everyone’s.
• A fine or polished steel will true a bent edge but won’t restore one which is worn.
• A medium, coarse, or diamond steel, will create a coarse edge and an uneven bevel. While the knife will cut, it will cut more like a saw than a knife.
In a thread about knife choice a Chef Talk member argued that a cook may use a steel to keep her knife sharp; preventing it from ever getting dull; and thus never needing actual, more aggressive sharpening.
It occurred to me the subject of dulling itself — what it is and what to do about it — can use a little demystification.
Q. How does a knife get dull?
A. All work and no play.
Okay, with that out of our systems we can move on to three real phenomena, deformation (bending out of true), corrosion and wear.
• All knives dull eventually;
• All knives eventually need to be sharpened if they’re going to become or stay sharp;
• A steel is not a good way to sharpen a good knife.
Before we get into this, start by visualizing the cross section of a properly sharpened edge as a V.
Bending:
The cross section of a rolled or waved blade can be compared to a y.
Edges bend from impact. More often than not it’s impact against the board, but sometimes it comes from cutting through anything hard. Cutting through bones will do it nearly every time.
Bent edges are commonly described as “rolled.” That can be refined somewhat into waving and rolling. While the difference is only a matter of degree, it’s significant as a practical matter. A waved edge (my term, and not universal) isn’t pushed over as far one which is rolled. If you’re visualizing the cross section as a “y”, roll or wave depends on the degree to which the tail is bent.
The practical part of the distinction comes in the mending. Assuming there’s not too much asymmetry or the knife alloy isn’t too hard – it can be easily repaired with a few passes on a rod hone (aka “knife steel”) which trues the edge. For more about steeling, see here.
The further the edge is rolled, the more truing it weakens it. And an edge which is rolled beyond a certain point won’t straighten on a steel, instead it will fold over further. This means treating severe rolls as you would a chip and sharpening them out.
Corrosion:
Carbon alloys are more reactive than stainless alloys and consequently are far more prone to corrosive blunting. Reactive alloys blunt in a couple of ways.
Passivation (not really corrosion, but what are you going to do?) forms deposits on the surface. In his essay Knife Sharpening Experiments, John Verhoeven describes “Debris Deposit burrs.” You can visualize the cross section of an edge blunted in this way as a U
Actual corrosion, e.g., rust, eats away at the metal and weakens it causing it to break very easily. The breaks give the knife a toothy, WWWWW profile (not cross section). In addition to the other undesirable aspects of too much micro-serration, the edge is inherently weak. Each tooth is subject to bending or breaking.
Frequent steeling will keep the metal fresh and relatively free from corrosion. But, even a polished or ultra-fine steel will scuff up the bevels, and the edge itself – creating (you guessed it) too much micro-serration.
The best practice – and again this presumes knives which can be profitably steeled – is to use a fine, ultra-fine, and/or polished steel as frequently as necessary; and going on to bench stones, an Edge Pro, or other abrasive method as soon as necessary to keep the knife very sharp.
Wear:
Wear is simply erosion by another name. In the same way water flowing over a stone eventually rounds it by removing material grain by grain and wearing away the edges, so normal use wears down the edge – which you’ll be kind enough to remember is very thin as a result of sharpening.
Please visualize the cross section of a worn edge as a U, just like a debris deposit burr.
The only solution is to sharpen using proper sharpening gear appropriately. What “proper” and “appropriate” mean is a very long subject in itself.
Just to kick the subject off, sharpening means using an abrasive to create an appropriate shape while revealing fresh metal. While you can true an edge, and even scuff it up enough to give it a little bite with a fine to polished rod hone it does not actually sharpen.
Because their narrow contact areas create so much force and because their aggressive surfaces remove blade material so quickly medium steels, coarse steels, “diamond” steels, or any carbide sharpener, etc., are not appropriate for sharpening good knives.
BDL
The Dulling Thoughts by Cook Food Good, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
Tags: blunting > carbide sharpener > chantry > corrosion > diamond steel > dulling > knife steel > knife wear > rolling > sharpening > steeling > waving
Comments
One Response to “Dulling Thoughts”
Leave a Reply
WHO IS BDL, Boar D. Laze, or whatever the hell his name is?
A Brief Biography:
Ex-Navy Seal; Ex-Victoria’s Secret model; Turned down a three-way with Sophia Loren and the young Marlene Dietrich (as in the Blue Angel) because had other plans; Knows who killed everyone in The Big Sleep, and why; Chaired the work-group which invented Time, Space, Gravity, Fire and Holiday Sweaters; Prefers Dickel to Jack.
What is Cook Food Good?
What’s this site about? It’s about a lot of thingsForcing myself to work out issues relating to writing a cookbook: COOK FOOD GOOD: American Cooking and Technique for Beginners and Intermediates.
Getting feedback on my work from you.
Discussions on basic and not-so-basic techniques. The recipes here are very technique driven. Similarly, the idea behind the book is to be far more about the how than the what – with the goal of teaching you to create your own recipes and tweak other people’s, confidently and successfully.
How to cook better, as it relates to you (and me too). That is, taking a beginner or advanced beginner to good, restaurant quality. Mostly this will be (more or less) French technique and (more or less) American food. But only mostly, more or less.
Recipes for this, that and the other.
Knives and all about sharpening them (which have somehow become a subject on which I frequently get asked for advice): How to choose and how to use.
The first Cook Food Good Blog was hosted by the website, Chef Talk. However, CT, removed its blog section. If you’re interested in bad writing, poor punctuation and ancient history, you’ll find the old CT posts archived here. One thing about posting on CT, was that it acted as a sort of language and attitude super-ego. Don’t count on it here. This is naked id.
October 18th, 2010 @ 6:55 am
Wonderful ..thanks a lot for posting a good informitive blog