all ceraminc tiles, mounted in between to tiles maybe?
Your idea will not hold well and may be dangerous if you slip in shower and hit the shelf. Built-ins are better and safer.
To do it properly, you will have to tear out a section of the shower wall which will allow you to properly install the shelf frame. It will probably end up being much larger that the shelf bracket because it needs to be securely fastened to a supporting member probably connected to wall studs at both ends. And once secured, the entire area refinished in tile. Unfortunately you will probably not be able to match the existing tile, so you may have to re-tile the entire wall or even the entire shower, depending upon how important the finished appearance is to you. As you can see, this project may approach or exceed the effort required to completely redo the entire shower. So my recommendation is to put a shelf pole in the corner or use a hanging basket of some sort to hang from the shower arm. It is really up to you. Good Luck.
The shelf could only appear to have been made from tile. The tiles are mounted on a subframe, covered with cementitious board and adhered with mortar, typically. With new construction (or major remodel), this is pretty straightforward; you'd just plan it in to the framing and finishing. With an existing shower, I'd have to say No, to this thought, because there'd be nothing to mount the tiles properly to. If you do get that far, you can get tiles with a specially shaped edge, called a bullnose that won't show the underside of the tile's body (an unglazed edge) for the edges of a surface, like a shelf. Grout can also be used to hide those 90 degree angles, if the bullnose tiles are not made to match the tile you are working with. Hope that helps/
