Transparent parts

Transparent parts have always been a little difficult to get right for me.

In the distant past, I painted them with normal paint, which totally ruined the transparency of course. 

Then I started painting them on the inside (still with normal paint), which kept the idea of transparency, but no more then that.

Ideally, I'd find a way to make it appear as if there's a lightsource behind the part, but that might be overreaching.

For now, I'm painting the inside with transparent paint, which exists in practically all paint brands. When dry, I will coat one with aluminum foil, just to see the difference with the other part.

(Yes, one of the parts is broken. This Enterprise is clearly cursed, but if you know the Enterprise C's story, that's no surprise)

Below is my test card for the transparent blue paint.

On the right side, I mixed 1:1 transparent blue with glaze medium. The result is rather pebbly.
On the left side, I mixed 1:1:1 transparent blue, matt varnish and thinner. This result is smoother. Not sure whether the varnish is better than the glaze or if the extra thinner did the trick. (Maybe I should start skipping steps during experiments and not change 2 variables at the same time.)