Mother of Pearl, two-hole, sew-through button. Lovely iridescence — rough shell showing on under side — perhaps this can be used to identify the source type of shell, but I don’t know what it is. Perhaps someone will help out. Or I will try to look up later. NBS Medium.
The above is based on the National Button Society's Classification System.
WRBA Button Album encourages discussions across various button groups, in-person or online. Please reach out to us with additional information or suggestions.