(backup from Coticule.be)


Questions often asked

  1. How does a Belgian Blue Whetstone compare to a Coticule? (a story about garnets)
  2. I have read somewhere that not all Coticules are equally suitable for razor honing. Is this true?
  3. Is there a difference between “Vintage” Coticules and recently mined ones?
  4. Are there any coticules that are completely unusable for razor sharpening?
  5. What size Coticule should I buy to hone razors?
  6. Do I really need a Coticule for sharpening a straight razor?
  7. How often do I need to “lap” my Coticule?
  8. What’s the deal on “Kosher” Coticules? Do they really perform better than the rest of them?
  9. What’s the “grit” rating of a Coticule hone?
  10. What is pre-dulling a razor? What is the purpose of it?
  11. How can I repair a nicked leather strop?
  12. How can I repair a Coticule?


1. How does a Belgian Blue Whetstone compare to a Coticule? (a story about garnets)

The Belgian hones (Coticule and Belgian Blue Whetstone, commonly abbreviated to BBW) are very closely related. They are mined together. Actually is is impossible to extract any Coticule without also extracting massive amounts of BBW. Traditionally, Coticules were always backed by a piece of BBW. Some bonded together by nature, but most of them glued together by man. The main reason for this is to reinforce the Coticule part with the stronger Blue stone. Nowadays, Coticules are backed with a piece of Portuguese Slate, because it is more cost-effective to use easily available slate tiles for backing a Coticule than to produce labor intensive backing stones out of BBW rocks. The BBW stones are now sold separately, because they posses honing qualities of their own. Both the Begian hones are used with “slurry” This is an abrasive milk raised on top of the hone by moistening the surface with water and rubbing it with a small piece of Coticule/BBW The slurry of the Belgian hones contains spessartine garnets. These garnets are extremely hard mono-crystals with a very typical shape.


They are hard enough to scratch steel. A slurry is not  made of garnets only. It also contains water (obviously), and a great deal of phyllosilicates. Phyllosilicates are minerals that are much softer than steel. These minerals bonded the garnets together before they were abraded off the stone by rubbing with the slurry stone.
On a hypothetical note, that explains what we have found in frequent observations, small garnets can easily sink in the steel. Larger garnets can’t sink so deep in the steel, because the honing pressure is spread out over a wider surface area. Try scratching a table with a spoon. Now try the same with a fork (Don’t send your wife or mother to me when you run into trouble over this important experiment;-)) Back to the garnets: with the size of the segments at the garnets’ surface being roughly the same, smaller garnets are less rounded than larger garnets. That makes smaller garnets more “spiky”.
Conclusion: large garnets leave slightly wider but also more shallow scratches, while small garnets cut more aggressively and deeper.

Coticules contain a high concentration of small garnets (5 to 15 micron in diameter): up to 40% of the entire volume of the rock.
BBWs contain a lower concentration of wider garnets (10 to 25 micron in diameter): up to 25% of the entire volume of the rock.

That makes BBW’s slower than Coticules and if we are aiming for serious steel removal during the first stages of honing, the average Coticule will perform a great deal faster than any BBW. Hence, if the choice to do serious bevel correction is between Coticule and BBW, pick the Coticule.

But there’s more to the picture:
The loose garnets in the slurry also abrade the very edge, while it plows through the fluid. The thicker the fluid, the higher the concentration of garnets (less water) and the more the thinnest part of the edge deteriorates from the impact with the garnets. That is a dulling action. At the same time, the garnets remove steel from the bevel sides, which is a sharpening action. As long as the edge is not very sharp earlier during the honing process, the dulling effect is negligible, because the tip is not as fragile. When the edge becomes sharper, the tip becomes more fragile and more prone to “slurry deterioration”. At a given point, there’s a limit where the edge looses as much keenness as it gains. You could hone the razor into oblivion and not ever get a sharper edge than this limit. One of the advantages is that you’ll never “overhone” a razor on a Belgian slurry, allegedly a common danger on synthetic water hones. With normal pressure and regular razor honing methods, we have never been able to see any evidence of “overhoning” on the Belgian hones.

At equal slurry thickness, a BBW with its lower concentration of less aggressive garnets, has a sharper limit than a Coticule.

Of course you could use thinner slurry on a Coticule, but for the inexperienced user it’s still easier getting more keenness of a BBW with slurry than hitting the same level on a Coticule with thinner slurry. With experience it can be done, however, and the BBW becomes pretty redundant for razor sharpening at that point.

When no slurry is used, but plain water instead, we get a different story. The garnets remain halfway or more embedded in the surface of the hone. A Coticule with its small garnets in higher concentration offers a very finely textured surface. The BBW, having more sparsely spread bigger garnets offers a less fine surface. Both hones become very slow. The BBW becomes so slow, that it seems to loose most of it’s honing qualities. It almost behaves like a piece of marble. It seems to very slowly dull the edge rather than sharpening it any further. That’s why it is not recommended to dilute the slurry to plain water on a BBW.
But Coticules just keeps on going, albeit at an extremely slow rate.

No slurry, no slurry deterioration either.

Obviously the edge won’t gain sharpness infinitely. As with any hone there still is a limit. That limit is defined by how deep the hone cuts in the steel. A hone that digs 0.5 micron into the steel will never define an edge thinner than those 0.5 micron. That’s one good reason to use minimal pressure during the final stages of honing. Coticules on water are slow. They remove almost no steel with each honing stroke. For that they can define very sharp edges. But they are so slow that it takes ages to catch up if you weren’t already at a very decent keenness when you decided to start working on water only.
A Coticule with water is a finishing hone. The majority of them can’t be used to make up for much neglected keenness earlier on in the honing process.

Last update on 2010-02-14 by Bart Torfs.

I have read somewhere that not all Coticules are equally suitable for razor honing. Is this true?

There are differences in Coticules, mainly in speed, and – correlating to that – the sharpness level you can manage to get from the hone when it’s used with slurry (an abrasive milk formed by a mixture of water and stone particles that are released by rubbing the surface with a smaller piece of Coticule). After the slurry stage, Coticules are always used with just water to refine the edge further and achieve the maximum keenness that can be reached. If done correctly that keenness will always be more than adequate for a smooth shave without any “pulling” discomfort.
During the slurry phase, faster Coticules level off on a less sharp limit than those who approach their goal at a slower pace. This happens because there is a higher concentration of abrasive garnets present in the slurry of fast Coticules and presumably they are also more aggressive. These garnets impact with the very tip of the edge, which causes it to loose some of its definition. The keener and fragile the edge becomes during the honing, the more it is affected by this process.
Slower Coticule display less off this behavior, and they generally do leave a sharper edge, coming right off the slurry stage.
But either way, slow or fast, the edge won’t be keen enough for a comfortable shave after honing on slurry. The slurry is just used to vastly speed up the first part of the honing. You always have to finish on plain water, preferably after some additional procedure to bridge the gap between the speed of slurry and the very slowly developing superior edge on plain water. There are several different options to pursue that, and they are presented in the razor honing articles found on www.Coticule.be
Most Coticules that abrade steel fast with slurry are also relatively fast with just water, so although they start with a handicap after the slurry stage, they are quite capable of catching up. Slow Coticules start with sharper results off the slurry, but they require more work to further refine the edge. Of course, there are not just two categories, but rather two ends of a universe, in which all Coticules are located. It must be clear by now, that every specimen of these natural whetstones asks for a slightly different approach and amount of work required to get the best results.

Last update on 2009-09-04 by Bart Torfs.


Is there a difference between “Vintage” Coticules and recently mined ones?

The answer is yes and no.

Till the second half of the previous century, Coticules have been mined at several different locations, all within the wider area of the Belgian town Vielsalm, by several mining companies. They all extracted raw Coticule rock from either one of 2 principle deposits, one extending from the village Regné all the way to the village Ottré, and another one extending from Salm-Château to the South of village Lierneux. There are a few additional, minor, deposits in the vicinity of the village Sart. The geological origin of all these Coticule deposits is the same. In spite of popular belief, the fomer mines were not abandoned because they were depleted, but because extracting the narrow Coticule layers is so labor-intensive that it eventually became no longer economically feasible in a shrinking market, with the laboring costs within a post-industrial country. It is in all fairness, not possible to assess the distinct properties of the hones produced by mining companies that closed long time ago. All the more because some wholesaling companies obtained Coticules from several mining companies and branded them with a large number of labels, sometimes marketed towards different user groups.

With the above in mind, the anwer is “yes”. There are vintage Coticules that come form layers that are currently not under exploitation, mined at locations that are long abandoned. Although it is not possible to identify them, “vintage” Coticule can be bought that originate from obsolete layers.

On the other hand, the answer is also “no”. From the currently mined layers, there is no single reason why the rock that is mined today would be any different from the rock that was mined 100 years ago. Coticule rock was formed approximately 480 000 000 years ago, a few 100 years more or less won’t make any difference. One could argue that “they picked the best rocks first”, but such an argument forgoes the fact that Coticule rock runs as thin layers almost vertically in the underground. Mining it is not a matter of grabbing what is best, but primarily a matter of what comes first and what is the easiest to extract.

Furthermore, elaborate comparison between a number of randomly obtained “vintage” Coticules and a large group of recently mined ones from all currently active layers, has not revealed any additional differences between “vintage” and “recent”, other than the variance found within the recent production. That variance is mainly a matter of abrasive speed. There are vintage Coticules as fast as the fastest recently mined Coticules, and that statement can also be made for the slowest Coticules in the spectrum. When it comes to edge finishing properties when the whetstones are used without raising an abrasive slurry, the differences between Coticules, both vintage and recently mined are too small to be quantifiable within any scientific bearing. Such assessments remain in the field of vague impressions, easily overruled by differences in the steel of the tool and other external factors that interfere with objective assessment.

The bottom line is that, unless you are a collector who esteems the historical value of a yesteryears whetstones, their labels and boxes, the word “vintage” is out of place. For sharpening practices, it is fair to speak about second-hand Coticules, and if you can buy them at a second-hand price, they are as good a deal as a recently mined one.

Last update on 2010-10-31 by Bart Torfs.

Are there any coticules that are completely unusable for razor sharpening?

No. This is a myth, launched by people that don’t know how to use them. It’s easier to say that the fault is in the hone…
Coticules do take a different approach than synthetic water hones.Translating the methods for synthetic water hones to Coticules yields poor results.
During one of my visits at the quarry I have seen that sometimes (rarely) quartz inclusions can be present in the raw rocks. Should these inclusions be present in the hone, they would cause damage at the very edge. That’s why the people at Ardennes Coticule cut the hones out of quartz free chucks, and if they do spot a small speckle of quartz in a hone they would never let that one to pass for sale.

Last update on 2009-08-29 by Bart Torfs.

What size Coticule should I buy to hone razors?

If money is an issue, opt for 150mm X 40mm, That’s wide enough for inexperienced fingers to keep the razor comfortably in touch with the hone, and long enough to perform a decent honing stroke. Anything more is a luxury, but the resulting edges will not be better.

Last update on 2009-08-29 by Bart Torfs.

Do I really need a Coticule for sharpening a straight razor?

No. It is a matter of preference. Just like you don’t really need a straight razor in order to get a clean shave, you don’t necessarily need a Coticule to sharpen a straight razor. There are many other options to put a great edge on a razor. But as straight razor shaving is the most artisan way to shave, we at Coticule.be feel that using a Coticule is the most artisan way to sharpen a razor. Coticules have a legacy that goes back to ancient Roman times. Some people find that appealing. Yet the shaving results of a Coticule edge can easily meet those obtained from modern high-tech synthetic hones and it remains one of the most skin friendly edges one can ever shave with.

Last update on 2009-09-04 by Bart Torfs.


How often do I need to “lap” my Coticule?

Many synthetic hones tend to glaze rapidly with abraded metal debris, sticking to the surface. Regular cleaning is required, to reclaim the full performance of the hone. Coticules, however, do not glaze. They are non-porous and therefor metal particles have no recesses to stick on to.

Another reason for lapping whetstones, is to reinstate a trued flatness. Yet it is not necessary to be persnickety about such flatness. For the honing of straight razors, that need perfect edges, because no razor can bluff its way through a shave, tests did not reveal any advantage for a mathematical flatness over a trueness “at first sight”.  For chisels, gouges, and other tools that have a way of wearing a transverse hollowing into a hone (as opposed to longitudinal hollowing caused by sharpening razors and knives, lapping needs to be done at slightly higher frequency. The wear rate of a Coticule depends on its purpose: sharpening chisels being one of the more eroding tasks and sharpening razors the least eroding. If you adhere to a few habits to keep your hone flat within good reason, depending on its purpose of use, it may stay serviceable during its entire lifetime, or only rarely demand lapping. These habits are:

1. While raising slurry, spend extra time on the far ends, notably the corners of the hone. Secondly, concentrate on the “high” spots. They can be identified because you’ll feel less resistance rubbing over them. At the lower spots, the rubbing stone will suck itself to the hone.

2. If possible don’t use the hone in the same direction during the regular slurry stage of honing. Once you arrive at the “refining” stages, do keep the stone oriented in the same direction. (You don’t want slight variations introduced in you honing at that point)

Should the Coticule arrive at a state where the out-of-trueness affects the quality of the resulting edge, it is time to lap.

There are several viable options:

1. Lapping with a dedicated lapping plate and abrasive powder, usually carborundum.

2. Lapping with a diamond hone in the 100-400 grit range.
Rub the lapping hone and the Coticule together under a slow running tap.

3. Lapping with sandpaper (in between 100 and 400 grit) on a known flat surface.
This can be done dry or wet. For dry use, spray-glue the sandpaper to a flat surface, and rub with the Coticule over it. Brush the sandpaper clean regularly.
For wet use, stick moistened sandpaper to a slick surface and work under a slow running tap.

To control for flatness, draw a pencil grind on the surface of the Coticule and check if you can remove the entire grid with just a few lapping strokes.

Last update on 2010-08-15 by Bart Torfs.

What’s the deal on “Kosher” Coticules? Do they really perform better than the rest of them?

Without being an expert in Chassidic Judaism, According to Orthodox Jewish Law, “impure” procedures are not allowed for the slaughtering of animals and the processing of meat. This means that Orthodox Jews are not allowed to use oil stones for the sharpening of the knives used for butchering practice, for oil may contain “impure” substances. Coticules that are harvested from deep within the Earth, are considered to be “pure”. “Kosher” means just that. In essence, every Coticule is a kosher one. Jewish law also prescribes that the animals must be killed with one cut. That calls for sharp knives and Coticules have always been acknowledged for yielding extremely sharp edges. Allegedly, the knives are stroked over the whetstone quite often – every few cuts -. This gets blood on the stone, which is no problem because Coticules are not porous. It is important however that the stone is completely free of cracks. For that reason, Coticules are preferred that appear completely perfec!
t. For the way they are used and and because we are talking about knives instead of razors, rapid steel removal is desirable.
Coticule manufacturers used to keep a small – Kosher – stock of stones that met those requirements for their Jewish customers. The designation “Kosher” recently started to lead its own life among straight razor users. Although there is no single reason why Kosher Coticules would put a better edge on a razor than “select” of “standard” grade Coticules, there is a higher demand for them than they are currently available. As a result prices for Kosher Coticules have escalated.

Last update on 2009-09-04 by Bart Torfs.

What’s the “grit” rating of a Coticule hone?

It’s a wrong question, but since so many keep posing it, let’s try to answer it anyway.
Coticules fundamentally differ from synthetic hones in the way they abrade steel. Depending on how they are used, the rate of stock removal is variable, the level of polish is adjustable, and how fine the edge can be defined is changeable as well. How on Earth can that be reflected in a short and simple “grit” designation? For a true understanding, an in-depth explanation about the abrasive particles of Coticules, explains where that versatility originates.


Cutting SPEED:

  • heavy, almost paste-like slurry: 1000 – 2000 grit.
  • regular, milk-like slurry: 4000-6000 grit
  • thin, misty slurry: 8000-12000 grit
  • water: 16000 grit – or even slower.


  • heavy, almost paste-like slurry: 600 grit, although less aggressive because the absence of a sawtooth pattern
  • regular, milk-like slurry: 2000 grit, although less aggressive because of the absence of a sawtooth pattern
  • thin, misty slurry: 6000-8000 grit
  • water: 10000 – 15000 grit


  • slurry: surface looks sandblasted on a micro-scale
  • very thin slurry: can be used to tone down harsh edges, very friendly for sensitive skin.
  • water: will add smoothness to the feel of almost any other polish level without removing keenness up to 15000 grit.

Last update on 2009-11-04 by Bart Torfs.

What is pre-dulling a razor? What is the purpose of it?

Pre-dulling a razors edge on glass is performed by lightly dragging the edge of the blade once over a glass object such as the rim of a drinking glass, or neck of a beer bottle, using only the weight of the blade and no pressure. Afterwards the razor should no longer shave arm hair; if it still does a second, equally light stroke may be necessary.

An edge can’t develop keenness on a hone before both sides of the cutting bevel are completely flat all the way up to very edge.
It is of equal importance that the edge is free from the damage that accumulates at a microscopic level from the impact with coarse beard hairs.

By dulling the edge, and then setting the bevel until the razor shaves arm hairs, we can be completely confident that the sides of the bevel are flat, and the action of dulling on glass can also help with the removal of damage caused from the impact with coarse beard hairs.

Pre-dulling is also recommended when honing newly fabricated razors, because  the bevels on these razors aren’t always as one might expect.

Also, when a bevel has been set on a synthetic hone, it can be useful to re-dull the edge before starting to work on a coticule. The reason for this is that  synthetic hones, up to 2K grit, leave a saw-tooth pattern on the edge of the razor and leaving this edge as it is might not result in the typically smooth coticule edge.

Other than that, there is no special voodoo to the practice of pre-dulling a razor.
It renders a razor barely below shaving keenness. So barely that it can be stropped to shave again. But, if there is any convexity in the bevel, or if the razor was previously honed with tape, then the very edge will not regain a shred of keenness on a flat, solid hone before the bevel is entirely set. Things become easy after the edge has been pre-dulled. No second-guessing, no worrying. If the razor starts shaving arm hair again the bevel is ready for the next step of your honing procedure. It doesn’t matter what bevel setter you use, or what the next hone or step in the procedure will be.

Last update on 2011-03-28 by Ralfy.

How can I repair a nicked leather strop?

Small nicks can be sanded flush with a good quality sandpaper of 300-600 grit. It is not advisable to use a pumice stone since it can leave grit in the leather.

If the cut resulted in a small loose flap, first glue the flap with cyano-acrilate (CA) glue (“wonder/super glue”). To do this, apply a very small amount at the bottom of the nick, press it firmly together, and wipe off any excessive glue. You will have to be very fast since CA glue sets very quickly, then sand smooth as above.

While not esthetically pleasing, small nicks do not compromise the performance of a strop.

Last update on 2011-03-28 by Ralfy.

How can I repair a Coticule?

Coticules are natural rocks. As such they are normally fairly low maintenance. They don’t glaze, don’t require frequent lapping, don’t de-laminate, they’re as good as impermeable and they don’t mind if you put water, oil, silicone lubricants or whatever on the surface. (some caution with acids would be in order though). But even so, some issues can sporadically occur. In this FAQ we offer an organized list of  possible problems and their solutions.
1. GLUE line separation
2. Natural separation
3. Cracks
3.1. Lateral cracks
3.2. Transverse cracks
3.3. Longitudinal cracks
4. Inclusions
5. Chips

1. GLUE line separation

The joint of a Coticule produced with nowadays methods is not expected to ever fail, since it uses a modern high performance, fully waterproof cement, similar to products used for swimming pool tiling. However on older specimens, that were glued several decades ago with less stable glues, it is almost predictable that the joint may fail at some point, given enough time to decay (100 years, plus or minus a couple decades).
When and if this happens, there is no need to panic. With the glues readily available on today’s market, it’s easy to bond both pieces back together. It is important that both pieces remain intact. Should haplessly the blue backing plate be broken, you could opt to glue the Coticule part to another backing: a tile, a paddle shaped piece of wood, or – if you want to honor tradition – a new piece of BBW. Should on the other hand the Coticule part be broken in 2 fragments, you can try to reassemble, but there is no guarantee that the transverse joint won’t interfere with the functionality of the hone. For a solution of that problem, see the paragraph about transverse cracks below.


First you need to scrape all the old glue off of both fragments. It’s a hide glue based adhesive, hence heat will soften it up. A hot air gun as used for stripping paint or even a plain hair dryer will help to soften the glue so you can take it off. As said, be extremely cautious not to snap the pieces. While working, the parts must be completely supported by your working surface. If the parts are not flat (old Coticules often separate during the lapping process), they can be supported on a plastic bag filled with damp sand.
Once you have both the surfaces to be rejoined clean (a bit of sanding might be in order), make sure they are dry before you continue to glue them back together. Almost any glue with filling capacities and reasonable water resistance will be suitable. Thin-set tilling mortar, skirting board adhesive, 2-component epoxy, glue-gun hot glue; are all capable of rejoining a Coticule with its blue backing plate. Follow the instructions of the product at hand. In general, apply a liberal amount of glue on one part (make sure it’s well supported), use a small glue comb to corrugate the coat of glue, and put the second part on top with a small sliding motion to assure an even and fully filled glue joint. It’s good if some excessive glue squeezes out at the sides. Scrape most of it off and lap the rest away later, when the glue is fully cured. In case of hot glue, preheat the parts with a hairdryer to buy some extra handling time.

2. Natural separation

In case of natural separation, which means that the Coticule separated at a lateral crack, either at the natural transition between the yellow and the blue part (which is the most prevalent occurrence of this rare problem) or at a crack present in the Coticule itself, the pieces will in 99% of cases still fit tightly together. If so, they can easily and perfectly be rejoined with CA glue (cyanoacryclate, also known as wonderglue/superglue).
In the unlikely event that the parts can’t be tightly fitted together, refer to paragraph 1 of this FAQ-article.

3. Cracks

3.1. Lateral cracks

Lateral cracks are cracks that show up at the narrow side of the hone. Often they can be squeezed together a bit and spring back when the force is released.
Sometimes such cracks run diagonally in the stone, to emerge as a longitudinal crack at (part of) the surface. If this happens the stone can be impossible to lap flat, because the lapping forces compresses the crack, only to spring back afterwards. This leaves you with an ever so slight raised part of the surface, which of course interferes with the honing functionality.


Option 1: Put the hone on its side, and use a couple of toothpicks to minimally pry open the crack. Pour in CA-glue, or even better use a syringe with needle to get it in. (Please wear safety glasses, you don’t want to accidentally have high-pressured CA-glue spraying in your eye!) Try to get in as much as possible. Ideal is when some of the glue starts emerging out the other end of the crack (if the other end is exposed). Remove the toothpicks and place the Coticule between a clamp, applying only the gentlest pressure. Give the CA-glue a day to cure. In a tight fit, CA-glue dries within seconds, but when it needs to fill the joint a bit, it takes considerably longer to cure. If the crack is expected to remain open for more than 2/10 ths of a mm, use special CA-glue with filling capacity. Or refer to option 2.

Option 2:

For larger cracks it is better to fill them with a hot glue. You can either use the sticks of a glue-gun type of hot glue, or prepare your own glue sticks according to the traditional composition. For this, melt together hide glue and beeswax (50/50) and pour it with aid of a funnel into paper tubes that you need to prepare for this purpose. To do so, roll a sheet of paper on your finger, using several revolutions. Fold the bottom 2 times, so that it can hold the glue once you pour it in and completely secure this cylinder with paper masking tape. Once the glue is poured in, allow to cool in upright position.
The use of these homemade hide glue/beeswax sticks is the same as glue-gun sticks:
Place the Coticule dry in an old skillet, and heat on a slow burner. Once it is hot enough, the Coticule will melt the glue as soon as you touch it with the stick. (Do not use the glue gun, but allow the Coticule to melt the glue by itself) Place the Coticule with the crack facing up and allow the glue to run into the crack. The heat will often cause a crack to open a bit further. Never try to hasten the cooling of a hot stone! Allow the stone to cool naturally in the skillet, rapid cooling of hot stone can cause it to shatter.
If you are using this method on an old Coticule, the glue that holds both parts together is the same as the hide glue/beeswax mixture. In this case you need to take special precautions to prevent the separation of both parts. Wrap the hone very tightly in several layers of aluminum foil, but as you make each wrap, use a sharp knife to make small incision of about 25mm along the crack somewhere in the middle. You need to end up with a tightly wrapped Coticule with only a small incision in which you will pour the glue. Fold the incision open a bit to properly expose the middle part of the track. If the crack comes out somewhere else, also make small incisions there to help evacuation of air, as the crack fills with glue.
Once cooled, trim of excess glue and lap the stone flat using a Diamond plate or wet and dry type sandpaper.

3.2. Transverse cracks

Transverse cracks are cracks running across the surface of the Coticule. They are not to be mistaken with Manganese lines, that are not cracks and have no negative influence on the functionality of the hone. Transverse cracks become annoying when the edge starts catching into them as it passes over during the honing stroke. This can be sensed very well, and obviously causes damage to the edge.
The solution isn’t ideal as you will likely still notice the crack as it will give a slightly different feedback after the applying the fix, but the Coticule can be expected to function again.


Take a square wooden block with sharp edges and fold a sheet of 80grit sandpaper around. Put the sanding block with one edge on top of the crack and start sanding. The goal is to replace the crack with a 2 mm deep V-shaped groove. A filler can be made from CA-glue, mixed with Coticule dust. You’ll need more Coticule dust than the one you got from creating the groove. Prime the groove with CA-glue and immediately apply the filler. Try to heap it up a little. Allow at least 24 hours to cure. Carefully lap the stone in a direction along with the prior crack, as to not stress is too much.
An alternative filler is to first fill the groove with baking soda (this is not the same as baking powder, baking soda is sodium bicarbonate) and pour CA-glue on top. Both respond to each other with an exothermic reaction, forming a hard filler.
Another excellent filler is to mix a quantity of Coticule powder with 15% (by volume) artistic plaster (plaster of Paris) Add egg yolk until the paste is soft and workable This allows a barely visible repair known to not affect the edge being honed.

3.3. Longitudinal cracks

Longitudinal crack are cracks than run lengthwise or almost lengthwise in the surface of the Coticule. They will usually not have any ill effects on the performance of the hone, and we suggest leaving them as is. For some ease of mind, they can be treated as lateral cracks, either by pouring in CA-glue, but without prying them open, or by the “hot skillet” procedure. Turning them into a groove for filling with any of the recipes explained at the paragraph about the treatment of transverse cracks will generally not be necessary.

4. Inclusions

Although a rare occurrence, it can happen, as the Coticule slowly wears down throughout the years of use, that a foreign fragment of rock emerges at the surface. Due to the composition of Coticule rock, this is in the majority of case any of a number of possible mineral crystals that are all considerably softer than steel, and mostly even softer than the overall hardness of the Coticule stone. In these cases there is no effect on the honing properties of the stone and nothing should be done. If however you experiences a hard clicking sound when the edge passes over the anomalistic particle, it is likely doing damage to the edge. This can be revealed by inspecting the edge under magnification. If this happens you will need to dig out the foreign particle. With aid of a loupe and good lighting it is not that difficult to dig out the particle with a needle. The tip of a needle can dig into the rock surrounding the hard particle easier than you might have expected and eventually the particle can be pried out. The resulting void can be left as is, or filled with one of the fillers from paragraph 3.2 – Transverse cracks.

5. Chips

Chipping can occur at the surface of a Coticule near the edge. If you see first signs of it, is best to create a more pronounced rounding of the hone’s edges. This can easily be done with 80 grit sandpaper on a sanding block. Further smoothing with finer sandpaper is recommended.

Last update on 2011-04-12 by Ralfy.