WHY YOU MUST BREAK IN A DIAMOND STONE
Why should you break in a new diamond sharpening stone? Learn how good quality diamond stones work, why loose grit can scratch your tools, and the easy setup process that protects your chisels and knives.
Diamond stones have revolutionized sharpening by hand. I use them for chisels and plane irons, router bits and Forstner bits. I even use diamonds on my power sharpening systems.
But when you get a new diamond stone or wheel, you must break it in before using it on your good tools or knives.
Here’s why.
Why New Diamond Stones Need Breaking In
I’m talking about quality stones like the MPower stones I use — not the cheap plastic ones with thin metal plates glued to the surface.
A good diamond stone starts with a steel substrate that’s machined perfectly flat. That steel is then placed in a solution of nickel and diamonds, which adheres to the surface through an electroplating process.
What you end up with are millions of tiny diamonds embedded in a thin layer of nickel.
But not all of those diamonds are embedded equally.
Some sit deep in the nickel, with just their tips sticking out like tiny icebergs. Others are closer to the surface.
The deeply embedded diamonds are the ones that stay put long-term. On a well-made stone, most diamonds are locked in with about two-thirds of their mass buried in the nickel, making them very difficult to pull out.
Even on a good stone, though, a few diamonds won’t be anchored deeply. Those loose diamonds will come off the first time you use the stone.
Click to enlarge. Right: Diamond stone unused. Left: Diamond stone after use.
Pictures taken from scienceofsharp.com
If you’ve ever seen microscope images of a brand-new diamond stone compared to one that’s been used for a few minutes, you’ll notice small empty sockets in the nickel where diamonds have pulled free.
Those loose diamonds are incredibly tiny — you won’t see them rolling around — but they can leave deep scratches in your tool edges that take a lot of work to remove.
That’s why breaking in a stone matters.
What “Breaking In” Really Means
Breaking in a diamond stone simply means removing those loosely embedded diamonds before you sharpen anything important.
Thankfully, it’s easy.
Here’s how:
Grab an old tool or any piece of hardened steel.
Rub it over the entire surface of the stone for about 30 seconds.
Use light pressure — let the stone do the work.
That’s it.
Don’t bear down hard. That’s a general rule with diamond stones anyway. Heavy pressure can dislodge more diamonds and shorten the life of the stone. These stones cut extremely well with light pressure, and they’ll last a very long time if treated properly.
After about 30 seconds, the few diamonds that weren’t locked in solidly will be loose. Rinse them off.
I use water with a rust inhibitor mixed in. Plain water is fine too — just make sure to dry your stone completely afterward. Anytime you use water, there’s a risk of rust, and you don’t want that.
One Minute That Saves Your Edges
Breaking in a diamond stone takes about a minute, and you only have to do it once.
But it’s an important step — especially before using a new stone on your good tools or knives.
If you skip it, those loose diamonds can leave scratches that make sharpening harder than it needs to be.
Do it once. Do it right. Then enjoy clean, consistent sharpening.
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