I have a 'mid-century' (circa 1965) clamshell and slate go stone set that has the usual yellowing streaks on the lined sides of the clamshell stones, and which I want to make white again (or at least whiter). I tried following the sparse and vague directions available on the Web at KGT and Sensei Library websites, such as soaking the clamshell in warm, soapy water and then rubbing them with a soft cotton cloth, with no effect. I also tried 'ultrasonic' cleaning using a SoniCare toothbrush after a soapy soak, again with no observable change. I have read that soaking in egg (whites only, or yolk too?) can remove the yellow, but I would like to know of others experience before I "get cracking" Anyone with experience in 'de-yellowing' clamshell are heartily encouraged to reply, so I can once again see the whites of my clamshells Thanks in advance!!

Hello,
Once the dirt and oils get into the grain (and make the shell yellow), you can't clean it with simple methods like egg whites or detergent. You'll need to send the stones to Mr. Kuroki for professional cleaning.

From my knowledge, the only way to properly restore the shells would be to remove the wax finish in order to get into the grain. DON'T DO THIS!!! Leave it to a professional.

Mr. Kuroki will use hydrogen peroxide to clean the shells BUT I don't know what percentage or for sure what method he employes.

I purchased some size 25 stones from Yahoo auctions when I lived in Japan, and to my surprise, found that they were Hyuga clamshell. Sadly, they were in abysmal shape, deep yellow lines and lots of dirt. I sent them to Mr. Kuroki, and aside from one or two shells that couldn't get all the yellow out, they came back looking just like new. Here's a link to the forum showing the end result of his cleaning (Sadly I don't have any pictures of the original condition):

viewtopic.php?f=20&t=7885

Here's a link to his Japanese cleaning site:
http://www.kurokigoishi.co.jp/onlinesho ... index.html

Just send him a message and he'll let you know how it'll work with international shipping and such. Hope that you can get your shells cleaned and looking like new again