10k was not marked on British jewelry before 1854. Indicating the gold frame (or at least the clasp) marked 10k was made before 1854. The style of Clasp is called a "C" clasp because the catch part looks like the letter C and is the earliest type of catch however it is still in use today and can also be found on modern jewelry.
The Cameo looks like a composition cameo. Usually the backs of composition cameo are flat but wannabe shell cameo is trying hard to be convincing with its concave back which would be closer to its antique shell cameo counterpart. If you look at the reverse - the shape of the concave is not at all natural, it looks too technically well done. Like a remmed out plastic composite might look. The surface of the front also looks too shiny. Shell cameo have more of a matte texture and surface. Wendy I would say a very well thought out composite cameo with an antique style subject in relief.
