Original yongzi set
Ancient book describing the making of yongzi
Handcrafting yongzi in the furnace
Yongzi in the furnace
Viewing the rich green translucent finished black yongzi stone
Chen Zude 陈祖德 admiring a black yongzi stone
Chen Zude 陈祖德 describing yongzi in a calligraphy scroll as “National Treasure Yongzi, Sacred Product of Go” 国宝永子，棋中圣品
Many people have heard of and may have bought yunzi 云子 go pieces, but probably few have heard of or seen it’s big brother yongzi 永子.
From wikipedia on yunzi:
The production of yunzi started in the Tang dynasty and reached its peak in the Ming and Qing dynasties; the total verifiable history of yunzi spans at least five hundred years.
Among yunzi, most famous was the yongzi (永子) manufactured by Yongchang Fu (永昌府, today the city of Baoshan, Yunnan) during the Ming dynasty. It was said that after a fire broke out in an imperial treasury, one of the keepers, who was from Yongchang Fu, discovered that melted pearls and jade had a special luster. When he returned to his hometown, he fashioned yunzi out of the agate and amber for which Yongchang Fu was famous. These yunzi went on to be prized by the literati and were offered to the Emperor.
…Today in Baoshan there are still people who have antiques dating from the Ming dynasty; among those there remain one and a half original yongzi sets.
Due to war and civil unrest towards the end of the Ching dynasty, the method of manufacture of yongzi was lost. Fortunately a center for the research on Yongchang culture and yongzi was founded in 2003 in Baoshan (Yunnan, China). In 2009, the manufacture method was finally recreated. In 2010, the trademark “yongzi” was registered in China and the quality tests passed and certified.
The black stones are described as translucent green like high quality jade while the white has the look of creamy ivory. Made from a combination of agate, jade, amber and other materials, it has been admired as the most desirable go stones by the ancient Ching Dynasty go players. With such rare materials used in it’s formulation, no wonder it’s rare and expensive. I’ve only seen one advertisement as of April 2012 in China for a set of yongzi stones at a cost of RMB18800 (almost USD3000). The advertized stones are size 22.5mm (±0.5mm）in diameter, and 12mm(±0.5mm）thick. Hopefully they will get a bit cheaper as they become more well known, but doubtful as the material costs are probably quite substantial and with the stones being handcrafted in a furnace.
I am however not sure if the current formulation contains lead or not as the ancient book in the second picture does describe the manufacture of the original yongzi stones as containing lead 铅.
I do not own a set of these stones and have only reported what little material I can find.
For a more in depth article on these stones (in Chinese) check: http://sports.sohu.com/20120418/n340908850.shtml
Found some more pictures and info on yongzi on a Chinese forum.
The last two pictures are comparisons between yunzi 云子 and yongzi 永子.
According to the owner of the above set, yongzi has a much better feel in your hand, being at the same time exquisite and yet comfortable. The bottom is very smooth with no unsightly bumps or cavities. Yongzi is also much tougher and resistant to shattering. The owner dropped a piece of yongzi from a height of 1 meter above concrete and it did not suffer damage.
The owner says that the factory retail price for a set of yongzi with bamboo bowls is RMB6860 and for a set with mahogany 红木 bowls is RMB16800. Those were the prices when he visited the factory at the factory.