Yunzi Stones Sizes, Single Convex

[Manchu]

I see YMI market single convex Yunzi stones as "Size 3," or 5.7mm thick and 22mm in diameter. They apparently also once sold "Size 4" single convex Yunzi at 6mm tall and 22.5mm thick. They are no listed as out of stock.

Does anyone know about this size scale? Or about YMI selling "Size 4" stones?

[bogiesan]

Give them a call. Great customer service, usually.

[skydyr]

My understanding regarding the single convex stones is that the size refers to the diameter, not the thickness as with double-convex ones. The larger stones (size 5?) are, as I recall, only really suitable for Chinese sized boards.

[Manchu]

That makes a lot of sense, considering the advertised difference between Sizes 3 and 4 is only .3 mm in thickness (which I kind of wonder about anyway, as other sources advertise Size 3 Yunzi stones being 6 mm thick) but all of .5 mm in diameter.

I was hoping to find some thicker single convex Yunzi but perhaps there is no such thing?

Also - do you know a good vendor for Chinese boards (assuming you mean on with square line spacing)?

[skydyr]

I suspect that the process for making single convex yunzi basically involves dropping globs onto a flat surface and letting them cool, so you can't really make them thicker or thinner than the surface tension of the material allows.

I've never looked for a Chinese-style board, which is the square style you're thinking of, so I can't say who is a good vendor.

[Inkwolf]

I suspect that the process for making single convex yunzi basically involves dropping globs onto a flat surface and letting them cool.

Right you are, and you can see them doing it in this video from the factory, at about 2:07
https://www.youtube.com/watch?v=rPdk6PbFbZk

...and from a wider angle at 4: 07.

[Manchu]

The flat surface in question is recessed at the desired diameter and, one suspects, at least to some degree, depth. The depth could be increased to create a thicker stone. Is it the case that the Chinese simply do not care for thicker single convex stones? Along the same lines - I wonder how old Yunzi really is, how widespread it was used, and what other materials have been used in China for go stones.

In any case, I put the question about Size 4 single convex Yunzi stones to YMI and will repost their answer here.

[Bonobo]

Manchu, cf. the Wikipedia article on Yunzi.

Regards, Tom

[Manchu]

YMI's speedy response:

Thank you for contacting us. Unfortunately, we are no longer carrying the size 4 Yunzi single convex stones. We do plan on carrying a larger size 5 stone in the future (6mm thick and around 22.5 - 23.5mm diameter). However, we do not currently have timing available for this item. It may be many months before we are able to offer this stone. Sorry for this inconvenience. Please contact us if you have any questions. Thank you for your interest.

[Manchu]

More from YMI:

Can you tell me about the size system you use? Is it correct that this system measures diameter and not thickness? Also, is it possible to get single convex Yunzi stones that are thicker than 6mm?

You are correct. For the single convex stones, the sizing system is for diameter. Size 3 stones are around 22mm diameter, while the size 5 are larger, at around 23mm diameter. Unfortunately, I am not aware of single convex Yunzi stones which are thicker than 6mm.