Mum's Button

When I came across an entry for Tiny Tuesday on a theme of Buttons I remembered my mother's button tin, which, as a child, I trawled through for entertainment and, after we sold the house, retrieved my favourites before anyone else laid a finger on them.

Others I do recall having been on her dress or a coat but not this one, it was solo, not part of a set and, if it had been worn on clothing, it was way before my time. This always fascinated me; a button in the form of a goldfish bowl? Why?

Thanks to host  MaryElizaR for jogging the memory.

Edit: We saw a brilliant sun pillar at sunset but neither camera would pick it up - so frustrating.