Yellowed Yunzi stones

[Farodin]

Hi everyone,

I recently received a full set of second-hand single-convex Yunzi stones, and the white stones have become slightly (but noticably) yellow, which is most visible when placing them alongside my other set of white glass stones.

I was searching for how to return the Yunzi stones to their original white state, but all the results I've found only speak about how to whiten shell stones, which in that case is done by using a diluted solution of hydrogen peroxide. For those of you that are more familiar with maintenance of Yunzi stones, have you ever come across yellowed yunzi stones, and do you know whether they should be treated in the same way as shell stones (i.e. with hydrogen peroxide)?

I can upload pictures later if need be, as right now the stones are soaking in soapy water for their first round of cleaning.

EDIT: Added images below. Stones on the left are glass stones, the stones on the right are the Yunzi stones in question (after washing). I'm wondering now, is this "yellowish tint" normal for Yunzi stones?

https://imgur.com/j2dhkLR
https://imgur.com/cBGFiaQ

[EdLee]

Curious to know if H₂O₂ also works for:

https://en.wikipedia.org/wiki/Yunzi

[Farodin]

EDIT: Added pictures to the original post.

[gowan]

The Wikipedia page cited by EdLee suggests that older "white" yunzi may have a yellow or green tint. Your stones might be older type. Another thought, maybe the yunzi were oiled and the color comes from the oxidized oil? Maybe try washing the stones using gentle detergent and water?

[bogiesan]

They have not yellowed with age or exposure to light; they were made in that color. There are four type so f Yunzi, designated ABC&D, distinguished by two colors and two shape: old (cream or old cloud), new (bright white), flat, and biconvex.

[Farodin]

Thank you gowan and bogiesan!

Knowing that this set of Yunzi stones was simply made this way makes me appreciate the beauty of them much more.