Take a closer look at the transparent glass tiles in this installation. Do you see the perfectly spaced ridges? Those are actually trowel marks caused by not flattening the thinset during installation. During installation of transparent glass tiles, you must flat-trowel the thinset so ridges are no longer visible.
Installations always should have trowel ridges except in cases like this. The ridges exist to create creates an even base of ridged mortar. When a tile is placed, the mortar compresses to provide a complete bond between the tile.
Extra planning must be taken when installing glass tiles. Size, backing, facing, and application are important to consider. Some tiles are transparent, or semi-transparent, while others may have a painted coating. You must also consider the color of thinset, the flatness of installation, type of thinset used. The thinset mortar has to be applied continuous and flat or those inconsistencies will show through the tile.