To print parts which looks like glass, I have checked different print settings for PETG. 

Overview Settings:

Results:

No printed part, indipendent of the settings, looks like glass without grinding and polishing. 

The most promising result I got for item 4 which is printed with 4,5mm/s and a layer height of 0,1mm. Without distance to a text, item 4 is more or less transparent (picture A). After increasing the distance to the text, also item 4 is not transparent without grinding and polishing (pictures B).

After grinding and polishing item 3 and item 4 are transparent. But in a high distance only item 4 is transparent (pictures C).