<p>I intend and would like to print a transparent hemisphere. I have a Taulman T-Glase clear 1.75 mm filament and I have XTC-3D.</p>

<p>You can read this interesting page, <a href="http://taulman3d.com/t-glase-optics.html" rel="nofollow noreferrer">Hacking t-glase to look more like glass!</a></p>

<p>First question, what kind of printing settings should I use? Should I go for a low infill percentage or a high one? Should I go for line or hexagon? I would say 5% line but perhaps there is a better setting.</p>

<p>Then, how should I use XTC-3D as mentioned on the above link? I'm a little bit confused how it can make the part more transparent.</p>

Refraction of light is caused by changes in medium or angle of inflection. Any changes in medium will cause refraction, as such to be the most clear you would not want pockets of air. This means that if you are printing single layer 0% would work. The best appearance would most likely come from 100% infill as there would be no changes in the medium. The epoxy you linked to appears to smooth the surface, The smoother the surface, the clearer it will look. It is the same reason why you don't see clear textured mirrors or windows.