It's a really good start. I applaud you for getting the painted symbols and lettering very neat. It also looks very thick, which is a good thing, as I have seen a few thin lexicons, and some of them don't look as nice.
A few things I'd like to mention:
-The spine of the book is very square and flat, where as in the reference it is rather rounded.
-The silver bits look like they're coming off a little. Also, the glue looks like it leaked from underneath the pieces, as well as residue on the surface. Maybe you could clean it off with a damp cloth?
-The embossed symbol on the back could be a little more raised and defined. Otherwise, the shape looks about right.
-I'm not sure how to explain it, but the part where the silver plates and the cover of the book meet, there is a visible glue seam (at least I think it's glue...), and although that place should be defined, it should be indented from the curved spine of the book, whereas the glue makes it look a little sloppy. Nothing a little paint can't fix though.
I think that it's really nice looking otherwise, and I like the black material you used to cover the book with. Good job!