Thank you for the replies for the fixing.

Cheers

水氣搞到氧化！

This can happen in high humidity areas over time. Much easier if you live near the coast or on the peak.
If it is only on the basket, then it's no big harm.
One can scrap and sand them off with a steady hand. With a bit of spray paint, it can look like new again.

請問有無師兄見過Sonus Faber Amati Homage 高中音單元裏有很多白色好似鹽結晶體在上面，很硬及很難清除！
用什麼方法才能清除呢？謝謝！(如圖）