How to Tell If Used Clamshell (Hamaguri) Go Stones Are Genuine
I work making and grading go stones, and one question I get a lot is: "I bought (or was given) a set of used clamshell stones. How can I tell if they're real?" So I've put together some points you can check yourself, without sending them off for appraisal.
- Stripe pattern (shell grain)
Genuine shell stones have natural stripes (growth lines) on one side, and no two stones are exactly alike. Plastic "clamshell-style" stones usually either have no stripes at all, or every stone in the set has the identical pattern. Placing a stone on your phone's flashlight makes the stripes much easier to see. Compare all the stones, and if the patterns look stamped out identically, be careful.
- Scratches and chips
Shell naturally tends to develop small edge chips over the years. Minor chips are nothing unusual, but stones with large chips, whatever the material, should normally have been rejected at the grading stage.
- Uneven whiteness
Genuine shell has a slightly creamy white that is consistent across the whole stone. If part of a stone is extremely white while another part looks dull, it is likely low-quality material or a damaged stone.
- Weight
This is the quickest check. Plastic stones feel noticeably light in the hand. Even without a reference stone to compare against, simply checking whether the weight varies between stones in the same set can tell you a lot.
- Hyuga vs. Mexican shell (a difference in origin, not real vs. fake)
Stones made from Hyuga (Japan) shell and Mexican shell differ slightly in their shade of white and in how the stripes appear. Hyuga stones have a slightly warmer white, with finer stripes that curve slightly in the middle. Mexican stones are a bright, almost bluish white, with stripes that run straight. Neither one is fake; it is simply the natural character of the material from each origin.