How to Choose Go Stones: Clam-Shell Grades, Thickness and Nachiguro Black Stones

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The short answer: grade and thickness of the white stones, plus the black

Choosing go stones starts with understanding the grade and thickness (go) of the white clam-shell (hamaguri) stones, and the quality of the black Nachiguro stones. White-stone grade is set by the fineness and evenness of the shell’s striations; thickness governs the weight and look of play. Balance grade and thickness to your use and budget.

Why the white stones set the value

Price and grade are set mainly by the white clam-shell stones. These are cut and polished from clam shell; the shell’s growth lines (shimame) — their fineness, evenness, and flow — are the measure of beauty. Being natural, no two are identical, and that individuality is part of the attachment they earn over years of play.

Clam-shell grades: yuki, tsuki, hana

• Yuki (snow): very fine, straight, even striations — the top grade, notably white and refined.
• Tsuki (moon): slightly broader striations but well ordered — an excellent balance of quality and price.
• Hana (flower): broader or more varied striations — fully practical and approachable.

Grade reflects the look of the striations, not playability as such — even hana gives the full feel of natural clam shell. Choose a higher grade for refinement and pride of ownership, a middle grade for practicality and value.

Thickness (go)

Thickness is measured in go; a larger number is thicker. Thicker stones give a weightier sound and feel and more presence, but need matching bowls and cost more (more material). Thinner stones play lightly, store easily, and cost less. A middle thickness is a sensible first choice.

Black stones: Nachiguro

Black stones are traditionally Nachiguro slate, a dense hard black stone that polishes to a deep sheen and contrasts beautifully with the white. Look for an even, deep black, a clean unchipped surface, and a size that balances the white stones’ go. Black stones are made slightly larger than white, to correct the optical effect that makes black appear to shrink so both look equal on the board.

Origin: Hyuga vs Mexico

Hyuga (Miyazaki) clam is the domestic peak — thick, beautifully striated stones, scarce and priced accordingly, chosen by connoisseurs and for gifts. Mexican clam supplies most of the market, in a wide range of grades and thicknesses, easy to choose for budget and use. In the end, judge by the combination of grade, thickness, and budget, and confirm origin labelling at a trusted shop.

The numbers to check before you buy

• How many stones: a standard set is 180 white and 181 black, 361 in all (Nihon Ki-in).
• What the size number means: it is the thickness of the white stone. The Nihon Ki-in gives 25 = 7 mm, 31 = 8.4 mm, 32 = 8.8 mm, 33 = 9.2 mm, 34 = 9.5 mm and 40 = 11.3 mm, and says stones up to about size 36 are the easiest to play with. Kuroki Goishi Ten offers clam-shell stones in even sizes from 28 (7.5 mm) to 50 (14.3 mm), and says 30 to 36 is generally the easiest thickness to hold between the fingers.
• How much larger black is: only slightly. The standard white stone is 21.9 mm across and the black 22.2 mm — 0.3 mm wider (Nihon Ki-in, Kuroki).
• Where Nachiguro comes from: Kamikawa-cho in Kumano City, Mie Prefecture. The Mie Prefectural Museum describes the deposit as a band about 4 km long there. Despite the name, it is not from the Nachi area of Wakayama.
• Grade names depend on origin: the Nihon Ki-in lists Hyuga shell in three grades (yuki, tsuki, hana) and Mexican shell as yuki, tsuki and jitsuyo (“practical”). The Hyuga suwabute clam from Okuragahama beach is now almost exhausted, which is why most stones today are cut from Mexican shell.
• Bowl size follows the stone: Kuroki sizes its wooden bowls against the slightly larger black stones — large (about sizes 20–30), extra-large (30–35) and super-extra-large (36–42) — and the Nihon Ki-in says an extra-large bowl holds stones up to about size 35. Shops use these names differently, so give the seller your stone size rather than a bowl name.

More detail: Go Stone Sizes Explained, Clam-Shell Go Stone Grades, How to Choose Go Bowls and Suwabute or Mexican?

Sources. Nihon Ki-in, “Igo zatsugaku”; Kuroki Goishi Ten on go stones and go bowls; Mie Prefectural Museum, “Nachiguro-ishi”. Checked 2026-10-06.

FAQ

How do I decide between grade and thickness?

For refinement and pride of ownership, raise the grade; for a weighty sound and board presence, raise the thickness. For everyday value, a middle grade at a middle thickness.