Charming Antique French Kiln-fired Enamel Buttons, Now Cufflink Pair in Original Box

Spectacular pair of cufflinks made from what would appear to be 4 Napoleon III era kiln-fired enamel buttons. Shown from back, you see the silver connector. I’ve worn these several times to rave reviews, and have kept them for decades thinking I’d wear them again. They’re in a period English jeweler’s presentation box, and I found them in England. I’m not certain if the box and cufflinks were always together, but it would appear so. Full measurements noted on the photos.  

Very good to excellent condition from box to enamel, really very little sign of the age, yet these are last half, 1800s. I’ve always thought them a pair of cufflinks made up from lovely French enamel buttons, and not a flaw to them. I suppose it is possible they might be English kiln-fired enamel on bronze or heavy brass plaque – are you able to tell the difference? I know button collectors seek after these, and it appears to me they could be very easily returned to a set of 4 antique buttons.