What has happened with Mrs. Rosa Bud's mother's heirloom?

We find about this topic in the last novel written by Charles Dickens, The Mystery of Edwin Drood, chapter 11. It is a wedding ring that belonged to Rosa Bud’s mother and now owns Mr. Grewgious. He will give this wedding ring to Mr. Edwin Drood as if he were to propose Mrss Rosa Bud for engagement. But he refused the next day to propose. He just wanted a friendship relationship with Mrss Rosa Bud. And further, we don’t know what happened to this heirloom. Can you give me some clues about his faith? And I want to know where to find written about this. Some supposed it was cast in a quick lime and it does not suffer any damage. Where I should find out more about this?