Shapton Kuromaku vs. Glass Stone vs. Rock Star: A Detailed Comparison

Shapton G7, Glass Stone, Kuromaku, and Rock Star water stones

Shapton is a renowned brand in the world of sharpening stones, known for their high quality and ease of use. With the recent addition of the Rock Star line, they now offer three distinct series to cater to different preferences: Kuromaku, Glass Stone, and Rock Star.

Why Choose Shapton Sharpening Stones?

  • Faster sharpening: Shapton stones are packed with premium abrasives, leading to fast sharpening.
  • Long-lasting durability: The unique binder composition ensures the abrasives wear evenly, maximizing the lifespan of your stones.
  • Splash-and-go convenience: No soaking required! Simply splash some water on the stone and you're ready to sharpen.
  • High-quality performance: All Shapton stones are crafted with meticulous attention to detail, guaranteeing consistent and predictable results.

Understanding Shapton Stone Sizes

Shapton G7, Glass Stone, Kuromaku, and Rock Star water stones

Glass Stone Seven (G7): Smallest sharpening surface of 160mm x 37mm (6-1/4" x 1-7/16"). Good for portability, sharpening knives or small tools, and using them as handheld stones.

Other lines: Standard size of 210mm x 70mm (8 1/4" x 2 3/4"). A very versatile size for any sharpening task.

Shapton G7, Glass Stone, Kuromaku, and Rock Star water stones stacked to show thickness


  • Glass Stones HR and HC: 5mm + 5mm glass backing,
  • G7 stones: 7mm + 5mm glass backing
  • Rock Star stones: 10mm
  • Kuromaku stones: 15mm

Even though they have thinner abrasives, the glass backing on the Glass Stones means you can use them until the abrasives completely wear away.

Visual Appeal and Grit Identification

The labelling of Shapton's water stones

The Kuromaku stones are color-coded sharpening stones. You can easily identify the grit from the color of the stone. The Glass Stones make grit identification even easier by printing the abrasive grit and/or micron size under the glass plate for easy legibility. The Rock Star stones have the abrasive grit size printed on the back and the grit and micron size is also printed on the side of the stone.

The swarf (metal reside) visible on the Shapton Glass Stone surface

Swarf or modern art?

The white color of the Glass Stone and Rock Star sharpening stones makes it very easy to see where you are removing metal from your edges as the dark metal particles that get removed contrast sharply against the stone surface. This also occurs with the Kuromaku stones, but depending on the color, the swarf may not be as clearly visible.

What Grits are Shapton Kuromaku, Glass Stone, and Rock Star Sharpening Stones?

Each Shapton series offers a range of grit options for different sharpening needs:

  • Glass Stone HR: 120 to 30000 grit (13 options)
  • Kuromaku: 120 to 30000 grit (10 options)
  • Rock Star: 320 to 16000 grit (10 options)
  • G7: Micron sizes ranging from 25 to 0.44 (9 options)
  • Glass Stone HC: 4000 to 8000 (3 options)
Shapton Stone Grits
Grits Kuromaku Rock Star Glass Stone HR Glass Stone HC G7*
120 x (white) x
220 x (moss) x
320 x (blue-black) x x
500 x x (also available with 10mm thick abrasive) 25 micron
1000 x (orange) x x
1500 x (blue) 11.5 micron
2000 x (green) x x
3000 x x 6.7 micron
4000 x x x 4 micron
5000 x (wine) 3 micron
6000 x x x
8000 x (melon) x x x 2 micron
10,000 x x 1.2 micron
12,000 x (yellow)
16,000 x x 0.85 micron
30,000 x (purple) x 0.44 micron

*The G7 stones only have the micron size of the abrasive printed on the underside of the stone. The grit size provided above is approximate.

What Are Shapton Sharpening Stones Made From?

All Shapton stones utilize aluminum oxide ceramic abrasives bonded with a magnesia binder. While the ingredients remain similar across the lines, slight variations in the recipe create distinct sharpening experiences.

For example, the Glass Stone and Rock Star stones are the same kind of stone, but Shapton modified the molding and pressing process. Some advanced users might feel a slight difference to the Rock Stars compared with the Glass Stones, but Shapton considers the Rock Star to be a thicker version of the Glass Stones without a glass backing.

The Glass Stone and Rock Star recipe creates stones that are slightly harder and finer than the Kuromaku stones. It’s a small difference and whether it's better or worse will come down to user preference.

Shapton Glass Stone HC with a carbon steel knife

The darker grey Glass Stone HC sharpening a hard carbon steel knife. The regular Glass Stone HR in the background shows the color difference.

Shapton also created the three Glass Stone HC stones. They’re all fine grit polishing stones, designed to put a final edge on quality high carbon steel tools. The Glass Stone HR sharpening stones will still work on these tools, but the HC stones have been specially formulated for users who want to get the most out of their high-carbon steel edges.

What Accessories Are Available for Shapton Sharpening Stones?

The Kuromaku stones all come with matching color plastic cases. These cases are great for storing the stone. They also double as a stone holder, with rubber feet on the bottom and a space on top for the stone.

Shapton Kuromaku sitting on top of its case next to a Rock Star stone in its open case

The Kuromaku storage case doubles as a stone holder. The Rock Star optional stainless steel case is for storage only.

The Rock Star stones are available with an optional stainless-steel case. This stylish case will protect your Rock Star stones when not in use and include stickers for labeling the case for quick grit identification. The Rock Star case is for stone storage only, and, unlike the Kuromaku plastic cases, it does not double as a stone holder.

Shapton Kuromaku in the Shapton Stone Holder with a Rock Star stone and Glass Stone next to it.

The Shapton Stone Holder works with all of Shapton's full-size stones.

Since the Kuromaku, Glass Stone and Rock Star stones have the same surface size, they all fit the Shapton Stone Holder.

Shapton Glass Stone Field Holder Kit.

The Shapton Field Holder Kit also includes 500/2000/16000 Glass Stones.

The Glass Stones will also work with the Glass Stone Field Holder. This will hold up to three Glass Stones and function as storage and a stone holder. It’s available on its own, or part of a kit that includes the Glass Stone 500, 2000, and 16000 grit stones.

Shapton Glass Stone Seven Knife Sharpening Kit.

The Shapton Glass Stone Seven Knife Sharpening Kit has everything you need to start sharpening.

The G7 Glass Stones are too small for either of Shapton’s stone holders. However, the Glass Stone Seven Knife Sharpening Kit includes a stone holder specifically for G7 stones. It also includes three G7 stones (the 25-, 6.7-, and 0.44-micron stones), a diamond flattening plate, and a marking pencil to help you ensure your stones are flat.

The Shapton Diamond Lapping Plate is a great option for keeping all your Shapton stones flat. Shapton also has a Cast Iron Lapping System that lets you match different surfacing compounds to the grit of the stone you’re flattening. You can also flatten your Shapton stones with other flattening stones or lapping plates.

Shapton also makes a Sharpening Pond that will contain the slurry created during sharpening.

Finding Your Perfect Shapton Stone

Ultimately, the best Shapton line for you depends on your individual preferences and sharpening needs. Here's a quick breakdown:

Kuromaku: Ideal for those who appreciate the color-coded grit system and the cases with a convenient built-in stone holder.

Glass Stone and Rock Star: Offer a slightly harder and finer sharpening experience, with versatile stone holders and high-contrast white surface for easier visualization. The smaller G7 stones offer a cost-effective way to enjoy this line of stones.

With its diverse range of high-quality sharpening stones and thoughtfully designed accessories, Shapton has something for everyone. Explore the different lines and discover the perfect way to keep your blades razor-sharp.