So here is how it can be done - I took quite a few pictures of the making of this Olive mirror - Using the reversed - or inverted method : Because I use materials of different thickness, I build the mosaic upside down. This can be a little tricky, but you get used to it.
It all starts with the drawing - here on a sheet of white paper - on top of which I laid a sheet of plastic. You don't really need to do this, but it makes the finishing part easier.
Now I glue the tiles on top of the plastic sheet - following the pattern of the drawing underneath.
I am using a water based and soluble glue.
All tiles were cut ahead of time. Here I start with the leaves and olives themselves. The background will come later.
And here is the final result - fruits and leaves, without the background. For this piece, I used shiny materials : various marbles, ceramics and granites
Finally, I have laid the background - Travertine. The Travertine has a mat finish that will nicely contrast with the shine of the other stones.
Now I have laid the frame around the piece, and I have flipped it - notice how you now can see the actual colors of the stones. There is quite some time involved in removing the glue from the surface.
Details of the piece. Several slightly different travertines bring more life to the piece.
Grouting - for this piece that included some gaps wider than 1/8", I used a sanded grout.
After grout clean-up, now you get an idea of what the piece will eventually look like.
Installation of the mirror
I still needed to stain proof the piece - which I did using a commercial stone sealer.
Et voila le travail...
Note : There are different ways to work this method. I do not always use the plastic sheet, you can use different sort of glues, and I did not show the part right before flipping the piece - it is very important there to use a fresh thinset - make sure it is not too old (that the bag has been kept well closed since the last time you used it). Also make sure you let the thinset set for a while before you flip. (48 hours is on the safe side) If you fail to do this : use a thinset that is too old, or rush to flip the piece, some catastrophes might happen, and you may have to spend lots of time trying to fix them. Thinset is not expensive, if you are not sure how old yuors is, dump it, go get a new bag...
Good luck