I was watching a decorating show last night and they showed a floating shelf hanging on a wall. I could not see how it was attached, at first, but they showed how to make one. They took a piece of dark shelving, any length and width. They marked a line about an inch or two from the front edge. They then used crown molding somewhat shorter then the length of the shelf. Cut each end at a 45 degree angle and took shorter pieces and mitered them at 45 degrees to match the front piece. the side pieces were flush with the back. They nailed and glued the side pieces to the front piece and attached them to the shelf. On a piece of masonite, they scribed the back pattern of the crown molding and cut it out. they made two screw keyholes for hanging on the wall and glued and nailed to the back of the shelf, the crown molding was painted the color of the wall which made it disappear from the eye. HTH

The floating shelvs that I have had experiance with are best decribed as a narrow box with the top fastened to the wall. You then put screws or nails in through the box side ie. shelf top to hold it on.