I purchased the Yunzi stones recently (double convex, 9.2 mm) and I like them alot. But I'm curious about the longevity of the color of the stones. I ask this because I'm wondering if the design of the stones cause color degredation.

As I understand it, Yunzi stones get better looking with time. They absorb the oil from your hands/fingers and start to get a shine to them.
(I'm by no means an expert though so I could be hallucinating about this)

they are just glass.

edit: otherwise, you're thinking of clamshell stones which do absorb the oils from your hands and may change color over time.

Yunzi stones are glass?! I thought they weren't.

The formula is a secret, and contains powdered rock and minerals. But it's somewhat glass-like, in any case, and if you've ever seen one chipped, it has smooth fractures like glass.

Since it doesn't have the smooth surface of ordinary glass stones, a light coating of oil is required to give them their full beauty. It can get that gradually from fingertips, or you can wipe them down with a little mineral oil from the start. If the black stones seem greyish, it's more likely they need a little oil, rather than that they are fading.

My white Yunzi stones seem to be yellowing slightly, but they probably just need washing after a year of use.

that's what glass is made from
http://en.wikipedia.org/wiki/Glass

I thought they were ceramic.

I think they are ceramic. I received a broken Go stone cleanly split down the middle. It was smooth as glass but felt like ceramic.

ceramic and glass have some similarities

the difference between ceramic and glass is whether or not its crystalline. glass is usually made from molten material, ceramic is not. but glass could be reheated to become partially crystalline

more info here: http://en.wikipedia.org/wiki/Ceramic


from what I've seen of yunzi making process -- they're glass.

either way, not much point to oil them, or worry about discoloration.

The difference in appearance between oiled and un-oiled Yunzi stones is drastic, at least for the black. Think of a pebble you pick up in the river because it's colorful, then when it dries it looks like just another rock. That's the difference.

I have played with normal glass stones, and Yunzi has differences, including the surface texture and translucency, even if they are technically glass.

Slate stones look good with a touch of oil on them, too, if they are looking old and grey and dry.

By the way, back on topic, I have one set of Yunzi stones that are from maybe the 80's or 90's, and they still have their color. They seem a bit more brittle than the new stones, and more likely to break and chip, but I don't know if that's age or changes in the formula.