I know, this is one of those Forge World heresy heavy weapon guys and this is a post about helmet lenses. But to be honest, that was the first thing I saw on this guy. I'm not a big fan of the weapon conversion (in fact I think it's horrible), but I love the subtle look to the helmet lenses done here.
When I paint my helmet lenses, I normally go much brighter overall. Here's the process I use (and even more important is when you paint them), but after seeing how the Forge World guys went with the much more muted look, I'm considering changing how I paint mine.
Now I do have a method I use when I want them to appear as though they are glowing and that is done by painting the whole lens a bright color and then washing it with a similar shade followed by a bright highlight in the very center of the eye to simulate the glow.
The Grey Knight troop above shows the effect. I used a bright blue-green color for the base color, wash it with GW Drakenhof Nightshade and then add a tiny bit of the original base color back into the center of the lens as the highlight.
I do like this look, but I don't like to use it all the time.
I already try to push the contrast when I paint my gems. I try to work from black all the way up to the bright reflected light on the bottom inside surface of the gem. if you look at the gem on the chest armour of the Eldar Guardian there, you can see what I mean.
I think I'm going to try and apply this higher contrast look to my helmet lenses from here on out. Instead of painting the lens a solid base color like I've done so far, I'm going to treat them like gems and work on adding that subtle reflected light along the bottom edge.
I don't see it saving me a ton of time, but I do see it giving me a better look overall and making the lenses appear more like glass instead of some non-descript material.
Make sure to check out these posts as they might help:
How to paint Space Marine helmet lenses
