People mix up two different things when they hear the words carborundum sharpening stone. One is a material: silicon carbide, a manmade abrasive crystal. The other is a brand name from 1891, stamped on stones for decades.
A carborundum sharpening stone is not a special shape or a special grit. It is a silicon carbide stone, old or new, branded or not.
A vintage stone with the Carborundum name on the box shares a company history. A fresh hardware store stone shares the same cutting chemistry.
This guide covers what silicon carbide does on an edge. It covers coarse and fine sides, oil versus water, and where this stone earns its keep.
What a Carborundum Sharpening Stone Actually Is
Edward Acheson discovered silicon carbide in 1891. He was experimenting with electric heat on a mix of clay and coke. The hard crystals that came out of the furnace turned out to be a new abrasive.
He named the material carborundum. He founded the Carborundum Company in Pennsylvania in 1894. It turned out grinding wheels, whetstones, knife sharpeners, and abrasive powder for decades.
The brand name outlived the company as most people knew it. Today the word gets used almost interchangeably with silicon carbide stone. If you want a plain silicon carbide sharpening stone now, you are buying the modern version of Acheson’s crystal.
Silicon carbide grains are hard and brittle. They fracture into fresh cutting edges as steel moves across them. That is why a carborundum sharpening stone feels aggressive under the hand.
That same brittleness wears the surface down faster than a diamond stone. It needs flattening sooner too. Most stones carry a coarse side and a fine side bonded into one block.
The coarse side resets a damaged edge fast. The fine side knocks down the scratch pattern the coarse side leaves. It still finishes rougher than a fine waterstone though.
Oil, Water, or Dry: What Owners Actually Do
Silicon carbide stones were built to run with a light honing oil. Older Carborundum branded stones assume that too. Oil floats away loosened grit so the surface keeps cutting instead of clogging.
Picking the type of oil that belongs on this stone matters more than people expect. A thick oil just gums up the pores. If oil based sharpening suits your bench, a dedicated oil stone for knives is the closer cousin to these blocks.
Plenty of owners run these stones wet with plain water or soapy water instead. Some sharpen them bone dry out of habit. Dry use is the one that causes trouble.
Owner reports describe the surface glazing over after long dry stretches. That glazing slows the cut until the stone gets cleaned or reconditioned. There is no single correct answer among long time owners here.
What a Carborundum Stone Suits, and What It Does Not
A coarse silicon carbide stone is built for rough work, not delicate finishing. Axes, hatchets, mower blades, and hoes are exactly what it was designed for. It removes steel fast enough to fix a chipped or badly rolled edge in a few passes.
It is a poor choice for a fine kitchen knife edge on its own. The coarse grit leaves a rough, toothy bite. That bite needs a finer stone or a strop to clean up.
Check picking a coarse stone for rough repair work if that heavy duty role is what you actually need. It is a different job from everyday knife maintenance. Our comparison across every stone type shows where silicon carbide lands next to oilstones, waterstones, and diamond plates.
Owner reports on old Carborundum stones describe aggressive cutters that rebevel a badly worn edge fast. Several note the stones still cut well decades after purchase. One thread called them blunt but dependable, useful and no frills.
Regular heavy use dishes the surface in roughly two to three years. That means it needs flattening like any bonded abrasive stone.
Modern Combination Stones Worth Considering
Genuine antique Carborundum branded stones are mostly a secondhand and collector market now. Condition varies a lot between listings. These two combination stones cover the same coarse to fine range in a new stone instead, and our other stone and abrasive reviews cover the rest of the shelf.
| Model | Type | Best for | Price band | |
|---|---|---|---|---|
| Sharpal 156N | Diamond, 325 / 1200 grit | Coarse repair work | $ | |
| King KW65 | Combination waterstone, 1000 / 6000 grit | Knife finishing | $$ | Price |
Sharpal 156N Dual Grit Diamond Whetstone
Best for Coarse Repair
Diamond plate | coarse 325, extra fine 1200 grit | case doubles as a base
This is the closest modern match to what a coarse carborundum stone was for. It resets a damaged or badly rolled edge fast. The diamond surface does not dish out like a bonded silicon carbide stone.
It suits axes, garden tools, and any edge that needs real steel removed. Skip it if you only maintain kitchen knives already in decent shape. A 325 grit face is more aggressive than most everyday sharpening calls for.
Pros
- Fast, aggressive coarse side for damaged edges
- Stays flat, unlike bonded abrasive stones
- Base and case is one compact unit
Cons
- 325 grit is too rough for finish work alone
- Needs a finer stone or strop afterward for knives
King KW65 Combination Whetstone
Best for Finishing
Waterstone | 1000 grit and 6000 grit sides | plastic base included
The King KW65 sits at the opposite end of the job from a coarse carborundum stone. It picks up after the rough work is done. It takes a 1000 grit edge up to a refined 6000 grit finish.
It suits kitchen knives and any blade where the goal is a clean edge, not heavy repair. Skip it if a chipped or badly rolled edge is what you are dealing with. It will not remove steel fast enough for that.
Pros
- Wide grit spread in one stone
- Included base keeps it steady on the bench
- Finish side gets genuinely sharp results
Cons
- Needs soaking or splashing like most waterstones
- Softer bond wears faster than diamond
Mistakes to Skip With This Kind of Stone
Do not run a bonded silicon carbide stone bone dry for long sessions. Then do not wonder why it stopped cutting. A glazed surface is telling you it needs lubricant or a light dressing.
Do not expect a coarse carborundum stone to finish a knife edge alone. Follow it with a finer stone. Review how to keep pressure even across the stone before you move between grits.
Do not assume every stone marked carborundum is silicon carbide from the original company. The name has been used loosely for over a century. Check the actual abrasive type before buying a vintage stone.
The bottom line: A carborundum sharpening stone is silicon carbide, whether it wears a vintage label or came off a shelf yesterday. For coarse repair work on axes, mower blades, and garden tools, a diamond plate like the Sharpal 156N does the job without the dishing a bonded stone eventually needs fixed.
Is a carborundum stone the same as a silicon carbide stone?
Yes. Carborundum was the original brand name for silicon carbide. The two terms describe the same abrasive material today.
Should I use oil or water on this stone?
Either works. Oil was the traditional lubricant, and plain or soapy water works fine too. Avoid long dry sessions since the surface tends to glaze over.
Can a carborundum stone sharpen a kitchen knife?
It can start one, especially a badly dulled or chipped edge, but the finish is rough. Follow up with a finer stone for a knife you actually cook with.
How often does a carborundum stone need flattening?
Owner reports on stones used regularly for heavy work describe dishing within about two to three years. Lighter, occasional use stretches that out.
Are vintage Carborundum brand stones worth buying?
They can be. Owners describe decades old stones that still cut well. Condition and wear vary a lot between secondhand listings, so inspect for dishing and chips first.
What grit is a typical stone like this?
Most pair a coarse side with a medium or fine side. Grit numbering was not always standardized or even marked on older stones. A tool for matching old grit numbers to modern ones helps when a vintage stone carries no number at all.