I found an old topic, Make your own stones, that has some ideas but doesn't appear to answer how it is done in practice.

I don't know how they are really made but there are some ways that I could think of. Probably these don't make all that much sense to someone knowledgeable about glass production , but here goes.

• Compression molding: molten glass is compressed by the mold and once the mold is removed the glass has to cool fast enough to not lose the shape.
• Transfer molding: molten glass is forced into an enclosed mold and left to set but the mold is removed in time to avoid cracks to form.
• Injection molding: mold is filled with glass batch, the mold is then baked and quenched (or whatever the process being used demands) to allow the batch to change to glass, glass that already has in the right shape.
• Rolling: molten glass is cut into gobs which are then rolled while cooling down, this could form the desired shape without applying much force.

Maybe more than one method is in common use, possibly none of the above?

Regardless of the method chosen, somewhere in there should be an annealing step.

Glass stones do get broken occasionaly, and I have always seen them break into two or three pieces. I'm sure that you do not want glass stones that shatter into dozens of sharp pieces.

The theory is simple: heat up to just below the point that the glass would flow and lose shape. Then cool slowly.

As a practical matter, if you are uncertain how slowly it should be cooled, just do it even slower.

The temperature for annealing is found by trial and error: heat a single stone until it loses shape. Then do your annealing a few degrees less than that.

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I've often wondered how glass stones are made. I have noticed that glass stones have more variation in shape and size than slate and shell stones. The misshapen glass stones might be due to molten glass changing shape after being removed from a mold. We know how the slate and shell stones are made, each stone is ground to shape. It seems clear that glass stones are not made the way slate and shell stones are. I notice less bad shape with yunzi (ha ha), but the material for yunzi seems to be something glass-like, ground quartz with some unknown additives. I have noticed that inexpensive Korean glass stones tend to have more misshapen stones and more expensive Japanese glass stones have fewer misshapen stones. This might be related to how the stones are made?

I do not know for certain but I would presume the method of producing glass stones is similar to that used for the production of glass marbles with a slight modification of the spiral forming screws that would from biconvex blobs instead of spheres. Japanese glass stones are superior to most others because of their manufacturing method includes precisely mixed glass recipes, precision manufacturing, and quality control. that produces precisely regular copies that are easily sorted for quality and uniformity.

I have many sets of lesser stones of korean and mystery origin that are misshapen, blobbish, irregular, chipped, and made of inferior glass that easily breaks and chips. And the white stones are streaked and spotted with impurities. Cheap stones are usually all glossy because the additional steps of acid washing the black to produce a matte surface is tedious and expensive.

Buy good stones. But you should probably buy every set of interesting and inexpensive go stones you ever find.

https://youtu.be/M4Pe-w9vXhg?si=8RKqUrl-JTrG1nu0
https://visit.houseofmarbles.com/news/the-marvel-of-making-marbles/

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David Bogie, Boise ID
I play go, I ride a recumbent, of course I use Macintosh.

If they are made with a machine similar to the rolling machine in the marble making video then that could explain something. I have observed that a common defect with glass stones is that they are too thick around the center between the two hemispheres. The center is flat when this occurs and the two hemispheres still appear to be concentric and have a good shape. Maybe this could be expect if they were made with a rolling machine.

I have also seen some sets that don't always have perfect shape on both sides. I don't know if this is simply a case of looking too closely or if it tells something about the manufacturing process.

Definitely annealing would be an important step. The exact material is also important, including anything that is mixed in or added on the surface. The stones would also be sorted depending on size and other parameters. All these details could hide some details about which methods are realistic.

Btw mirrors and lenses in cameras and telescopes are made by grinding glass, not so unsimilar to how shell stones are made, I wonder if any of those Japanese lens makers have ever made one-off Go stones.

"Btw mirrors and lenses in cameras and telescopes are made by grinding glass, not so unsimilar to how shell stones are made, I wonder if any of those Japanese lens makers have ever made one-off Go stones."

Have you watched the video clips of the artisans at Kuroki? Also clips of the Yunzi stone factory? Yunzi double-convex stones require a complicated multi-step process.

IN the marble-makers, annealing takes place along the entire length of the molding screws.

All of the previously mentioned glass molding and casting methods are certainly possible in the mass production of glass go stones. For a company that is making millions of pieces, economics of scale, ease of maintaining the machinery, raw materials, acceptable level of quality, and number of employees become determining factors in the factory's success.

Just to keep the conversation going, the many sets of glass go stones I've had over the decades have been wildly different. But Japanese stones are far superior to all the others when it comes to the objective factors: regularity, quality of the glass, and surface finish. The whites are flawlessly polished, blacks are uniformly acid etched with no irregular patches. Subjectively, I prefer the look and feel of the Japanes units, probably because my teachers all used Japanese glass stones (until I advanced to using their shells). Had I been raised on Yunzi, I might have grown up to like the flat, all-matte stones.

I acquired most of those weird sets by asking staff in little Korean/Chinese/Japanese neighborhood markets in larger cities. I spent anywhere from $5 to $25 for dusty boxes found under piles of stuff, happy to rescue them from the trash bins during the next cleanup of the shop's storage room. I also bought several $10 sets from Sidney Yuan (ye olde Yutopian Enterprises) and gave them away to aspiring newbies (ungrateful louts). Another topic: ING GOE stones; I ave away a lot THOSE, too.

Although they are getting more difficult to find, I suggest a set of cheap go stones belongs in every serious player's equipment collection. I usualy take mine along to venues where I know the floor will be concrete or tile.

Yes.

I especially like this one: https://www.youtube.com/watch?v=JghjOqvV0_o. I wished it was an hour long it is so soothing.

Less soothing but also interesting https://www.youtube.com/watch?v=BhPFLuLlCHQ, it is possible to select automatic translation as subtitles.

There are many other videos showing how the shell stones are made
https://www.youtube.com/watch?v=1VljuuMqR9k
https://www.youtube.com/watch?v=PJ7w9TzvSFE
https://www.youtube.com/watch?v=0QyDIY-F7SA
https://www.youtube.com/watch?v=-Xc2AwCIJbU

There is apparently less interest in showing how the slate stones are made, let alone glass stones. It is not the same level of craftmanship. I am just curious about how it is done.

I have seen a video of how proper yunzi stones are made but they are flat on one side (though I have played with bi-convex yunzi stones, that exists).

Thinking about how stones are flat on one side makes me wonder how the bi-convex form came about. It is lot of trouble to make that shape. It is much easier with all these materials to make something more like backgammon pieces.

I believe that the ancient stones in museums in Japan are flat on both sides, just disks. I don't know what they are made of. How the traditional half flat/half rounded yunzi arose is also interesting. It seems to me that both sides flat is easier to make and also easier to pick up. Completely speculation but I wonder whether the first playing pieces were pebbles found in nature and those would likely be rounded, like stones found on a beach which become rounded and shaped by water wave action. Such stones would probably be quite irregular in shape. Aesthetic sense and desire to reduce the visual noise would naturally lead to deliberately polishing and shaping. All speculation, of course.

I found a blog post with lots of pictures of ancient Go stones and equipment. I haven't read it, only glanced at the pictures, some of which I had seen before but many I'm sure I have never seen.

Interestingly, the blog post which is titled "A Pictorial History of the Game of Go" starts by stating that it is "perhaps not so interesting" since there many similar resources for Go. It then gives various links to Chinese language pages. All of the links that I checked were stale.

We are not the first to ask these questions, leaving me to wonder where the rigorously scholarly and peer reviewed research is hiding. It is also fun to speculate wildly.

Disks are far simpler to manufacture from cylinders of many different substances from wooden dowels to delrin, from clay to plastics. The point in time When craftsmen started to cut disks from slabs of stone suggests a new development in tools and the use of abrasives, not just to polish but to cut. Sophisticated stuff. Molten glass requires a different type of toolmaking and refractory processes, perhaps adapted from the established crafts of forging and casting of metals.

I have photos of seen ancient Japanese go stones that have swallows and doves engraved or painted onto them. They appear to be biconvex. I am guessing that some random go stone maker, perhaps employed at a royal court, who also played go, undercut some of his disks and found them easier to pick up.

Clamshells are an obvious choice but black slate is a bit of of a conceptual reach because the two sources of materials are so far apart and the manufacturing requires different tools. That is, cutting and shaping slate is quite different from cutting and shaping shells.

I’ve done lapidary work with various rocks and minerals. I have been a woodworker. and i have worked with clays and hot glass. I would much rather pay any price for well executed go stones than ever attempt to make my own!

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David Bogie, Boise ID
I play go, I ride a recumbent, of course I use Macintosh.

Maybe the ones from 'Shosoin Repository'? The ones with birds engravings are apparently ivory. I also found pictures of stones that are said to be made from quartz and serpentine.
Official webpage for Shosoin repository.
'Treasure' search result for "Go" with lots of high resolution pictures.