Thank you mongoct. That was a wealth of helpful information. One question, does silicon come in white or just clear? The tiles I am using said to use a white thinset so the glass tiles didn't show as a different color. Of course, clear wouldn't create a different color, but it might make the web backing more visible in the mirror. I do plan to grout so maybe the webbing isn't an issue. Thoughts?

100% white silicon is available.

I found this photo online, it shows an example of how you can see the back of the tile in the mirror reflection. The thicker the mirror glass, the more of the mesh will be visible.

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The color of the adhesive used to adhere the glass tile is more important the more translucent your glass tiles are. If your glass is pretty much opaque, then the adhesive color doesn't matter as much. The more translucent the glass is, the more important it becomes.

If seeing a little bit of the adhesive through the reflection in the mirror doesn't bother you, no worries. If it does, then to eliminate the reflection and without muddling the color of the glass tile, a better bet might be to paint the portion of the mirror that will be tiled black. Then adhere the tiles with a white silicon.

If your glass tiles are translucent enough to spec out using a white adhesive, then I also recommend back-buttering the tiles with white silicone before setting them.

That will ensure you get a full coverage of silicon between the tile and the glass. No entrapped air bubbles, no uncompressed ridges. Any bubbles or uncompressed ridges on the back of the tile can show through as shadowing when looking at the front of the tile.

I just did this in a bathroom I updated on the cheap because the mirror had black spots and was hard to replace without taking half the wall down with it. I got glass tiles from Home Depot, took them of the backing and cleaned off the glue that was left from the webbing. Then I used some Epoxy glue to glue the tiles directly on the mirror. The only problem was the area where the clips held the mirror in place. I removed them, except for one, which I couldn't get out (top left). Before:

After:

I was actually prepared to paint the back, but honestly, the reflection of the back was not a big deal since it was dark gray. So far, the tiles are still holding up.

The only problem was the area where the clips held the mirror in place. I removed them, except for one, which I couldn't get out (top left).

So what is holding the mirror up? Did it have glue in addition to the clips? I am used to the clips being the only thing that holds the mirror in place.

Yes, the mirror is firmly glued to the wall, which is why plan A, to replace it, didn't work without taking half the wall with it. Plan B was therefore, to glue the mosaic over the blackened edges. Also, I didn't have a tile saw to cut a small piece that would have fit where the last clip is.
However, others have removed the clips and used washers to hold the mirror up. Then you can glue the tiles over the flat washers.

Okay, I need a visual. How does a washer hold up a mirror?

http://www.sandandsisal.com/2011/01/how-to-frame-mirror.html
scroll down to the last picture

You can also google "washer holding mirror in place" or something like that.

Thanks for the visual. Not sure I get the point though, they make metal mirror clips that aren't any bigger than the washers.

These clips? I'd be interested in finding flat mirror clips that could be used to replace the current plastic clips on my mirrors.

Here is a link that might be useful: mirror clips

Do you know the name of the design of your tiles? I bought the exact same ones a few years ago for my mirror but I need replacements. I should have bought extras back then, and now I can't remember the name.

Post is almost 3 years old.