FAQ

The stones

Do Shapton stones need to be soaked in water before use?: No, Shapton stones do not need to be soaked except the very first time after purchase. We do recommend that on first use, you pre-soak the stone in water for five to six minutes to secure even smoother sharpening.

Do sharpening stones have 'best before' dates?: No, there are no time limits on when sharpening stones can be used.

What are the features of Shapton stones?: Shapton stones' characteristics include "High abrasive & sharpening capabilities", "Ready to use immediately" , "Reduced wear", "Long lasting" and "No smell".

What are the features of GlassStones?: The conventional image is that sharpening stones are large and heavy, but GlassStones are not only thin and light, but also strong, as layers of tempered glass are stuck together. GlassStones therefore have strong resistance to cracking or sudden breakage caused by external shocks such as being dropped.

I found some uneven colour on the surface of the stone I just bought. Is anything wrong?: No. It is in the nature of sharpening stones that spots or uneven colours appear on the stone surface. This is not a quality problem, and you can use the stone without concern.

What is the difference between the RockStar series and the KUROMAKU series?: The RockStar series comprises solid 10 mm sharpening stones, available as either standard models (with no case) or together with a stainless-steel storage case.
The KUROMAKU series comprises solid 15 mm sharpening stones, which come with a plastic storage case. Both series are available in ten different grit sizes, but the lineup differs.

What is the difference between the RockStar series and the GlassStone series?: The RockStar series comprises 10mm solid sharpening stones of a high quality equivalent to those in the GlassStone series.
The GlassStone series products feature 5 mm tempered glass laminated to 5 mm sharpening stones.*
The RockStar series has 10 different models, while the GlassStone series has a total of 17 types.
*Product no. 50106 features 5 mm tempered glass laminated to a 10 mm sharpening stone.

What do the markings on the side of RockStar products stand for?: The type of stone, the country of manufacture and the lot number.

What does 'class' refer to?: It indicates the approximate median particle diameter (size) of the abrasive material in the product, in micrometres.
When expressed in words rather than numerically, 'COARSE' represents the largest median particle size class, and 'NANO' the smallest.

What does 'type' refer to?: It indicates the type of abrasive contained in the sharpening stone.
HA: Mono-crystalline fused alumina
PA: Pink alumina
WA: White alumina
A: Regular (brown) alumina
CA: Calcined alumina
HPA: High purity alumina

Which face of the KUROMAKU series sharpening stones should I use?: You can use either face, but we recommend that you start on the side where no letters have been printed.

Some white marble-like patterns have appeared on the sharpening stone's surface. Is anything wrong?: No. These white marbled patterns can appear on the surface of a sharpening stone under certain conditions, depending on how the stone is stored. This is not a quality problem, and you can use the stone without concern.

Are there any blade materials that cannot be sharpened?: All blade materials can be sharpened except ceramics and superalloys.

The plastic case that came with the unit has broken. Can I buy a replacement?: Yes. KUROMAKU cases can be bought separately from the main product.

What are sharpening stones made of?: Sharpening stones are made of abrasives such as alumina and silicon carbide, combined with binders and other compound materials.

How does one remove burrs?: Place the burred side of the blade against the sharpening stone, then remove the burrs by gently sliding it along, without much pressure.

Is it possible to sharpen a kitchen knife with a nicked edge?: If the nick is large, remove it using a coarse stone of 40 micro and above (320 or below), then sharpen it using a succession of stones, moving from coarse to fine.

Why do I still see scratches on the blade even though I have sharpened it with a KUROMAKU fine stone?: If you polish it with a finishing stone after sharpening it with a medium stone, but there is still slurry adhering to the blade or your hands, the blade may be scratched by the rough abrasive agent of the medium stone. Because of this, when changing whetstone and moving to progressively finer sharpening steps, it is important to wash off any dirt produced in the previous step. It is not enough merely to rinse the blade and your hands: you should carefully and thoroughly wash off any films of dirt on your hands, fingernails, and the surface of the blade.

Should sharpening stones be used in a particular order?: The usual order is to start with coarser stones having larger abrasive grains, then move to finer stones with smaller grains.

How often should blades be sharpened?: That depends on the blade's material, purpose and frequency of use, as well as the level of cut you are seeking.
Our recommendation is to sharpen a blade whenever you feel its cutting ability has declined.

What are coarse stones of 40 micro and above (320 or below) used for?: Coarse stones are designed for adding an edge or removing large nicks on an existing edge.

Do Shapton stones come with a Nagura Stone?: No. Shapton stones do not need a Nagura Stone, and lapping with a Nagura Stone will leave the surface rough and ragged.

Is it OK to use oils with your sharpening stones?: Yes, it's fine to use oil with the stones. However, once you've used oil on a stone, you should always use oil with that stone.

Recent KUROMAKU stones look different from the designs bought in the past. Is there any difference in spec?: No. The only change was in the printing design, not in the quality or specs of the stones.

Recent GlassStones look different from the designs bought in the past. Is there any difference in spec?: No. The only change was in the printing design, not in the quality or specs of the stones.
Click here to see the before and after designs.

before

after

Should the Lapping Disc be immersed in water before use?: There is no need to immerse it in water in advance, but do wet it when using it.

Which of the surfaces on the Lapping Disc should I use, the flat one or the one with grooves?: You can use either surface - the grooved surface will give a slightly finer result.

How do I use the Lapping Disc to perform 'dressing'?: First wet the entire surface of the sharpening stone. Next, take the Lapping Disc in one hand, and dress the entire stone surface by making small circular motions, but without applying too much force. There is no need to dress it for a long time: only one layer of 'skin' needs to be removed for the sharpening stone to regain its original performance.

Do I need to keep water running constantly while sharpening a blade?: There is no need for a steady stream of water - you can sharpen your blades with just a splash of water on the stone surface. However, if you do let the water stream constantly, it means your hands stay clean while sharpening.

Does a build up of slurry create any problems when sharpening?: It is fine to sharpen blades without washing away the slurry, but as Shapton sharpening stones have a high abrasive content, they can be used equally well with no slurry present.

The GlassStone series includes two types each of the 4000, 6000 and 8000 sharpening stones. What are the differences between them?: They use different abrasive agents. GlassStone series 50603, 50703 and 50803 are recommended for sharpening composite steel blades, where steel has been forge welded with another metal.

Are any of the KUROMAKU sharpening stones recommended for normal household knives?: We recommend the Orange Medium (1000) sharpening stone and Wine Fine (5000) finishing stone. If you intend to use only one stone, we recommend the Blue Medium (1500) sharpening stone.

My sharpening stone no longer sharpens as it did when first bought - it slips and slides. What should I do?: It may have become clogged. We recommend that you try using a lapping plate.

When I use "KUROMAKU Purple" for sharpening, it feels wrong.: "KUROMAKU Purple" is designed to give an optimum, unprecedented cutting feel to the blade tip (around 1 mm), so it may feel strange if used with conventional sharpening methods.

I want to try using "KUROMAKU Purple", but the 'Precautions' state it should be used after "KUROMAKU Melon" － would it be OK to use it for sharpening after "KUROMAKU Yellow" instead, as this is finer?: That would be fine with high hardness steel, but for blades made from softer materials, please do use "KUROMAKU Melon". This is due to the stones' physical characteristics.

The lapping plates

How often should I lap the surface of a sharpening stone?: We recommend that you lap it any time a blade is to be sharpened. Keeping the sharpening surface in top condition helps maximize the sharpening stone's performance.

Can diamond sharpening stones from other suppliers be used to flatten your sharpening stones, or would this cause problems?: We have not tested what happens when diamond sharpening stones from other suppliers are used to restore our sharpening stones. Depending on the particle size and state of the diamond sharpening stone, it might not be possible to flatten the surface properly.

Can I use Shapton lapping plates such as KUBO, DGLP and NAORU to flatten diamond sharpening stones?: No. These lapping plates are not recommended for use with diamond electrodeposited sharpening stones because the surfaces can be damaged.

Is there a way to check whether flattening has been done correctly?: As a guide, use a pencil to draw a grid on the stone surface to be flattened.
Parts where the lines get erased show where the lapping plate has made contact, i.e. where flattening has been performed correctly.

I lapped the fine sharpening stone, but it no longer sharpens.: If the stone surface has been lapped roughly, you will be unable to sharpen blades well. The sharpening stone surface needs to be lapped to a mirror finish (when lapping a fine stone, use a combination of "NAORU" with "Fine Lapping Powder", or "KUBO", or the "Diamond Glass Lapping Plate").

What is the difference between KUBO and NAORU?: KUBO is made of cast bronze, with diamonds electrodeposited on its lapping surfaces. It has a front side for lapping sharpening stones, and a back surface for fixing damaged blades.
NAORU is made of ductile cast iron, and comes with lapping powders to be sprinkled on its surface before use.

What should I do if my KUBO's sharpening ability declines?: Diamonds do get worn out over time. If the KUBO's performance has declined, we offer a diamond re-electrodeposition service.

I used a brand-new "KUBO" to lap a fine sharpening stone, but the stone's surface is still rough, not like a mirror finish.: A brand-new "KUBO" may still have some diamonds protruding, so it's best to use it first to lap some medium sharpening stones a few times.

Where can I apply for the KUBO Re-electrodeposition Service?: Please, contact the dealer where your purchased your kubo.

Can a KUBO be used to flatten sharpening stones of any grit?: KUBO can only be used for flattening fine stones of 30 micro class or below (400 or above).

How long does KUBO Re-electrodeposition take?: The turnaround is usually about 1-2 weeks after receipt, but it can sometimes take up to a month or so, depending on the situation.

How many times can a Diamond Glass Lapping Plate be used?: A Diamond Glass Lapping Plate is usually good for around 1,000 to 3,000 applications.

Can a Diamond Glass Lapping Plate be used to flatten sharpening stones of any grit?: DGLP can only be used for flattening fine stones of 30 micro class or below (500 or above).

Can NAORU be used to flatten natural sharpening stones?: Yes, NAORU can be used to flatten natural stones too.

The lapping powders that came with NAORU have run out. Can I buy replacements?: Yes, the powders are available separately.

Can I use NAORU to flatten sharpening stones of any grit?: You can, but make sure you use a lapping powder that matches the stone's grit.

How should the NAORU be stored?: After use, use cold water to wash away any slurry or powder, then let the water drain away well before storage. Some rust may appear depending on how the product is stored, but this has no impact on usage.

I lapped the stone with "NAORU" and "Fine Lapping Powder", but its surface is still rough, not like a mirror finish.: If softening of the stone has progressed beyond a certain depth, you will be unable to lap it with "Fine Lapping Powder". In such cases, first use "Medium Lapping Powder" to scrape away the soft parts, then thoroughly rinse away any dirt and once again use "Fine Lapping Powder" to finish the stone's surface.

What does "Tomozuri" mean?: Tomozuri means to rub the surfaces of two stones or plates against each other.

Can lapping be carried out by rubbing stones against each other?: Yes, it can. In such cases we recommend rubbing three sharpening stones against each other, in turn.

Maintenance

Is it OK to soak your sharpening stones in water for a long time?: No. Don't soak our stones for more than 30 minutes, because this may cause the stone to become softer.

Is it OK to use hot water when sharpening?: No. Don't use hot water with our sharpening stones, because the water will cause extreme changes in temperature that can cause cracks.

Is it OK to use detergent with sharpening stones?: No. Don't use detergents with our sharpening stones, because they can cause changes in the quality of the stones.

Does leaving a sharpening stone outdoors cause any problems?: Leaving a sharpening stone outdoors is not advisable as this may cause it to deteriorate and crack. sharpening stones should be stored indoors at room temperature, away from direct sunlight.

Is it OK to dry a wet sharpening stone using a fan?: No, do not attempt to dry a sharpening stone rapidly by directly applying a fan or the like, as this can cause cracking.

Is it OK to clean sharpening stones in a dishwasher?: No - neither dishwashing machines nor dish dryers should be used.

I feel a stone's sharpening ability has declined since I bought it. What might be wrong?: One possible cause is deformation of the surface. We recommend you flatten it, to keep the sharpening surface in prime condition.

What should I do if a crack opens up on a sharpening stone?: Cracks can form when a sharpening stone is not used for some time, or if usage precautions are not observed. The main causes are sudden drying or extreme changes in temperature.
Shave off the surface at the cracked part. Cracks get deeper as they get wider, so it is important to do this at an early stage, while the crack is still small. If the stone is used in an extremely dry environment, we recommend keeping it in a plastic bag or a sealed plastic container, to prevent acute dry-out after use.

What should I do if a sharpening stone gets clogged?: We recommend using our Lapping Disc, a dressing stone.

How should I take care of my stones after use?: After using a stone, wash any dirt off with a brush or sponge. If dirt is left adhering to a stone, its sharpening ability can decline.

Is it OK to use sandpaper to flatten a sharpening stone's surface?: No, abrasive paper can leave a stone clogged, with the result that the blade slips and it is impossible to sharpen it.

What should I do if the surface is no longer flat?: Sharpening stones start deforming the moment they are used to sharpen a blade. Repeated sharpening then causes the flatness of the blade to be damaged too, mirroring the deformed surface of the stone.
Use a lapping plate such as KUBO, DGLP or NAORU to return the surface of the sharpening stone to its flat state.

My KUROMAKU fine stone has gone soft.: If you leave a sharpening stone immersed in water for over half an hour, or apply detergents and the like, the stone's surface will soften, or there will be qualitative changes - this is what has happened here.
Also, if you use a wooden sharpening base etc. of your own and this gets wet, the fine stone may absorb moisture from it and become soft.
If this happens, you will need to scrape the sharpening stone until a sharpening surface with the original hardness emerges.
In such cases, use "Medium Lapping Powder" to scrape away the soft parts, then thoroughly rinse away any dirt, and use "Fine Lapping Powder" once again to finish the stone surface.
Storing the KUROMAKU series in their special cases can also help prevent softening, but do wipe away any moisture inside the case first.

Should KUROMAKU sharpening stones be stored together with the white, spongy liner included when they are purchased?: No, the spongy liner (polyethylene foam) should not be used when storing sharpening stones after use. Polyethylene foam is a cushioning material used to prevent breakage during transportation, and if stones that are not completely dry are stored together with this foam, it may cause them to degrade.

Miscellaneous

How much do Shapton products cost?: We do not specify the retail price of Shapton products: please ask your Shapton dealer for their current price list.

Can Shapton stones be used outside Japan?: Yes, Shapton stones can be used anywhere. However, please note that particularly dry areas can cause the stones to crack.

What are the RockStar storage cases made from other than stainless steel?: Alongside the stainless steel they contain rubber and magnets.。

How does the RockStar stainless-steel storage case open?: Click here to see how to open the case.

Are any particular handling precautions to be observed with the RockStar stainless-steel storage cases?: Click here for the handling precautions.