Sharpening a Knife With a Knife? How to Sharpen Without a Sharpener

Yes, you can get a usable edge without a sharpener, but sharpening a knife with a knife is the weakest and riskiest of the usual tricks. The spine of a second knife is smooth steel, so at best it straightens a rolled edge the way a honing steel does; it doesn't remove metal, and it puts two blades right next to your fingers. If your knife is dull and there's no sharpener in the house, the unglazed ring on the bottom of a ceramic mug works far better, a honing rod fixes the most common kind of "dull," and fine wet/dry sandpaper on a flat surface can stand in for a stone.

Below you'll find each method step by step, what it really does to the edge, and why a proper whetstone is still the better long-term answer.

First, check whether the knife is dull or just out of line

Many knives that feel dull aren't worn out at all. In normal use the thin edge gets pushed slightly to one side. It still has plenty of steel, but it no longer meets the food straight on. That's a job for honing, not sharpening.

• Rolled edge: the knife cut well a few days ago and now slips on tomato skin. A few strokes on a rod, or one of the tricks below, usually brings it back.
• Truly dull edge: the knife has felt blunt for weeks, honing changes nothing, or you can see light glinting off the very edge when you tilt it under a lamp. The edge is rounded and needs metal removed.

Our article on when knives should be sharpened walks through the warning signs in more detail. Knowing which problem you have tells you which emergency method is worth trying.

Sharpening a knife with a knife: does it work?

The idea is simple: hold one knife still and draw the edge of the other along its spine, alternating sides, as if the spine were a honing steel. It's one of the most popular shortcuts online, so here's the honest version.

What it can do

The spine of a sturdy, softer Western knife can nudge a slightly rolled edge back into line. On a cheap, soft-steel knife you may feel a small improvement for a day or two.

Why we don't recommend it

• It isn't sharpening. The spine is smooth and not abrasive, so a rounded, truly dull edge stays dull.
• It's hard to control. Neither blade is fixed, the contact area is tiny, and the angle changes with every stroke. Uneven strokes can leave the edge worse than before.
• It's risky for your hands. You're working with two blades at once, close to your fingers, often in a hurry.
• It can chip hard, thin edges. Japanese-style knives have thin edges that don't like being knocked against another piece of hardened steel. A chip takes much longer to fix than a dull edge.
• It marks the second knife. The spine and the edge both pick up scratches and burrs.

Never rub the edge of one knife against the edge of another. It just damages both. If the spine trick is truly your only option, use light pressure, keep the stationary knife pointing away from you on a cutting board, and treat the result as a stopgap until you can sharpen properly.

Better emergency methods, step by step

1. The bottom of a ceramic mug

Turn a ceramic mug, bowl or plate upside down. Most have an unglazed, slightly rough ring on the base. That raw ceramic is a fine abrasive and the best emergency sharpener in most kitchens.

1. Set the mug upside down on a folded damp towel so it can't slide.
2. Hold the knife at a shallow angle to the ring, roughly 15–20° per side. For many Japanese-style knives, aim for the lower end.
3. Draw the blade across the ring from heel to tip with light pressure, as if you were slicing a thin layer off it. Make 5–10 strokes on one side.
4. Switch sides and make the same number of strokes.
5. Finish with a few light, alternating strokes, one per side.
6. Wash and dry the knife, and wipe the gray metal streaks off the mug.

The ring is fine-grained, so it works best on an edge that's only moderately dull. Pick a mug you don't mind marking, and skip any whose base ring is glazed or chipped.

2. A honing rod or steel

If you own a honing rod, you already have the best tool for a rolled edge. Hold the rod by its handle, place the heel of the blade against it at your usual angle and draw the knife down and along the rod so the whole edge passes over it, from heel to tip. Alternate sides for 4–6 light strokes each. Our guide to sharpening steel technique covers grip and angle in detail.

A ceramic rod does slightly more than a plain steel. The Samura ceramic honing rod, for example, has a 254 mm (10-inch) ceramic rod that polishes and adjusts the edge your knife already has. Hold the blade at 15–17°, the factory bevel angle of SAMURA knives. When a rod no longer helps, the edge needs a stone.

3. Wet/dry sandpaper on a flat surface

This is the closest substitute for a whetstone. Lay a sheet of wet/dry sandpaper on something perfectly flat, such as a thick cutting board or a sheet of glass, and wet it slightly. Start with a medium grit if the edge is very dull, then move to a fine one. Work like this:

• Pull the blade spine-first toward you, edge trailing, so the edge can't dig into the paper.
• Keep the angle steady and make the same number of strokes on each side.
• Feel for a small burr on the opposite side before switching sides. Slide a fingertip from the spine toward the edge to check, never along it.

Don't push the edge into the paper; it will cut straight through. And keep in mind that sandpaper grits use a different numbering system from whetstones, so the numbers on the sheet don't translate directly to stone grits.

4. A leather belt or a sheet of cardboard

Stropping polishes the edge and removes the burr left by any of the methods above. Lay a leather belt flat on the counter or use a piece of plain cardboard. Pull the knife spine-first, edge trailing, with very light pressure, alternating sides. A strop won't revive a truly dull knife, but it makes a freshly worked edge noticeably cleaner.

Emergency sharpening methods compared

Mistakes that make a dull knife worse

• Too much pressure. Light, even strokes do the work. Pressing hard rolls the edge or tears it.
• A wandering angle. If you lift and lower the spine from stroke to stroke, you round the edge instead of sharpening it.
• Uneven sides. Make roughly the same number of strokes on each side so the edge stays centered.
• Testing with your fingers. Slice a sheet of paper instead. A sharp edge cuts cleanly without snagging.
• Using coarse surfaces on good knives. Concrete steps, bricks and the edge of a car window leave deep, irregular scratches on thin, hard blades.

Serrated knives are a special case: none of these flat-surface tricks reach inside the scallops. See our guide on how to sharpen serrated knives instead.

Why a proper whetstone is the better answer

Every method above is a workaround. A mug base is a random piece of ceramic, a knife spine isn't an abrasive at all, and sandpaper needs a perfectly flat backing. A whetstone is made for the job, and that shows in the result:

• Consistent abrasive. A stone has a defined grit across its whole surface, so every stroke removes metal the same way.
• The right grit for each step. SAMURA groups its stones by job: coarse stones for correcting the blade angle, medium stones for starting and for light resharpening, and fine stones for finishing and polishing.
• Room to work. A wide, flat surface lets you sweep the whole edge from heel to tip in one controlled stroke, which is almost impossible on a mug ring or a knife spine.
• A repeatable angle. Water stones are soaked for 10–15 minutes and kept wet, and you sharpen one side until a burr forms, then the other. If holding the angle is the hard part, a sharpening angle holder sits on the spine and keeps the tilt constant.
• A real fix for real damage. A chipped or badly worn edge needs a coarse stone, such as a diamond stone, to reshape it. No emergency trick can do that safely.

If you only buy one stone, start with a combination stone. The Samura #1000/#3000 combination whetstone sharpens on one side and finishes on the other, and it's easy to use even if you've never sharpened on a stone before. Browse all whetstones, or pair a stone with one of our sharpening rods for maintenance between sessions. Our step-by-step guide on how to sharpen kitchen knives shows the full routine with a stone, rod or electric sharpener, and honing rod vs whetstone explains which tool to reach for when.

FAQ

Can you sharpen a knife with another knife?

Not really. The spine of a second knife can straighten a slightly rolled edge, much like a honing steel, but it doesn't remove metal, so it can't fix a truly dull edge. It also risks chipping thin blades and cutting your hands.

What household item can I use to sharpen a knife?

The unglazed ring on the bottom of a ceramic mug or plate is the most reliable option. Fine wet/dry sandpaper on a flat surface also works well. Use light pressure and a steady angle of roughly 15–20° per side.

Does sharpening a knife on a mug damage it?

Not if you use light pressure and a steady angle. The raw ceramic acts like a fine stone. It won't reshape a chipped or badly worn edge, though, and it can leave gray marks on the mug that you'll need to wipe off.

Is a honing rod the same as a sharpener?

No. A honing rod realigns and polishes the existing edge; a whetstone removes metal to create a new one. Use the rod regularly and the stone when the rod stops working.

Can I use these methods on a Japanese knife?

Use them with care. A honing rod and a mug base are the gentlest choices. Avoid the knife-spine trick and coarse surfaces like concrete, which can chip a thin, hard edge. Single-bevel knives such as a yanagiba or deba are best left for a proper whetstone.