under crescent & 2 dots for; Fa. J. M. van Kempen & Zonen, this particular mark used 1858-1924
For information about the history of Van Kempen see;viewtopic.php?f=5&t=28590#p70305
Minerva head or assay office mark with regional assay office letter C for The Hague.
The year letter perhaps gothic K for 1894.
Through the ages silver items are melted down for the silver to be used in a new product. Enjoy your rings.