Congrats on your finds- nice sixpence. The other is the back part of a two-part button. The face of the button (often domed) would most often be covered with material to either match or contrast with the garment it was being sewn to. The material would fold into the domed face which then snapped onto the back- which was sewn on where required. Very handy for dress makers- not sure how old? HH
yelnif