Small antique button. The centre is a black and white dome - not sure if this is agate or black glass with a white ring. This is held in a brass collar, surrounded by a rim of tiny cut steels individually rivetted through the brass base. Flat back and U-shaped shank. There is a tiny pin hole to one side (see last photo), otherwise in good vintage condition.

Size 9/16” (1.4 cm)