The connotation "sterling" indicates a given alloy. It is 925 fine, and should range between 915 and 935 fine. 900 fine silver is recognized as coin silver (even when used in flatware).
Knife handles are generally filled. A cement of sorts is one of the fillers I encountered regularly, as well as rosin. There is little silver in the handle, although certainly worth recovering. I used to dismantle them by beating with a hammer on an anvil, then tearing the silver away with side cutters. You need not be delicate about the process.
Be certain that the silver in question is, indeed, solid silver. Many of the Scandinavian countries have even lower silver fineness. I experienced it as low as 700 fine. As far as I know, it's always alloyed with copper. It is commonly marked as 700, 720, etc., up to 925.
Harold
