few things you can do to make this look better.
the wood mantle is a big one. remove the stone one and replace it. you can go to a big store or lumber yard and get a 2X6 wood (or 4x8) wood beam, have it cut to size. stain it. beat it up if you want it to look old.
Instead of paint, use a Limewash like Romabio. they have small containers that don't cost much. they come in diff light white/wash colors
You can do a lighter wash,
or a heavier coverage.
see the before down in the corner? This looks great. but notice whats done around it as well.
Heavier and rustic mortar wash/lime coating. wood mantle. this is easily done over your stone
styling your mantle (the wood one) and surrounding area, is key on making this type of FP look good
I don't think that black marble is the best match, UNLESS you go for the light wash. leaving as is doesn't really work.
The mantle. here are some photoshops
Has a nice stained wood beam mantle and a little millwork above it.
Don't pile on a bunch of small knick-knacks. do a piece of art, a cool mirror, and a few items to accuate it.
don't want to touch the stone? then fir it out w/simple wood pieces and do a diff material on top
you could now put up cement board and tile on it, or, you could do some wood shiplap, or a mantle surround
see how it's built out a bit? leave the stone around the firebox (paint it if you like) and then do the wood build-out. plenty of how to's.
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how to fir out and reface fireplace
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