Time spent pleasantly; making a replacement of an early style brooch for someone who had lost theirs. (suspected theft;... kind of flattering?)
I decided to put a roller-style catch on the pin for extra security.
One can just buy a machine-made catch and solder it on, unless one cannot be bothered going into the City to fetch it, in which case one must Make One's Own, which is what I did. Its not as perfect as a machine-made one, but that sorts of suits the piece, and it works very well indeed.
Open position; put the pin into the slot and then the tab at the top rolls down...
and locks the pin in place. Voila!