Here are two entirely different enamelled brass buttons.
One is large at 3 1/2cm with a sort of geometric design incorporating cream and blue enamel. The other is multi coloured with a floral design. It makes me think that it was a “practice button” as the colours and border design to me are a bit of a “hotch potch” (the computer doesn’t like that word!) when you look closely. (No rhyme nor reason) It measures 3 cm.