I know that generally Tom Bihn bags can be gently handwashed and air dried. But what about cork? I just spent a month and a half in China with my beloved cork and steel Imago and the cork insert is quite a bit darker except where the buckle protected it. I think it is grime rather than natural air darkening. I was thinking about trying a dilute solution of Murphy's Oil Soap, which is what we use to clean our cork kitchen floor. Is there a better recommendation?