Gaspare, thank you for your good info about enamel in rings.

As an addition, here a ring with niello that is often used to decorate silver with this typical nice black

Niello consists of sulfur, copper,silver and lead .
If niello has been damaged, you see little fractures ( pic 2 ) and worser, that can even drop out the ring..I have changed the pic 2 so you can see the cracks better.

1P1250619vd.jpgwc67kb.jpg (66.11 KB, 205 downloads)
3 1250472daACw.jpg (104.22 KB, 206 downloads)
4P1250461dCw.jpg (48.35 KB, 205 downloads)