I've discussed using pigments before and since then have used them quite a bit. Here's another type of pigment - Day-Glow. (Or Day-Glo.) The reason I prefer to use the term "Pigment" and not "Weathering Powder" is because these have more uses besides weathering.
In this article I'm going to compare using day-glo pigments to paint and briefly touch on why you can't replicate this look with normal paint.
I bought these ones from Forged Monkey (Massive Voodoo) but they seem to have changed around their store since then and don't appear to be selling it anymore.
Not to get too technical, but basically we see objects based on reflected light. An objects colour determines what light from the spectrum is reflected while other colours are absorbed and converted to heat.
Day-glo, neon and super-bright colours work by reflecting more than just basic colours. They actually convert other spectrums of energy to their colour, so when it's reflected, it's stronger. More intense. This is also why these colours seem to glow under UV or black light, because they're converting so much of that energy to visible colour. You can also get paints that only reflect UV light and are invisible otherwise.
(a source)
I decided to revisit some of my previous miniatures, most notably Mulg the Ancient, to attempt to intensify the magical effects and runes.
It's a different effect.
When painting glow effects, the brightest you can make regular paint look is by using white to simulate a bright-white glow in the center of an effect. You can see in the "Painted" examples how I've used bright paints with white highlights.
In the "Pigment" steps, you can see the difference when I've rubbed the day-glo powder in to the runes instead. (Before varnishing.)
That's just the first step, because it's still very powdery. I found that the final varnish phase really pulled everything together. Below you can see a final comparison of Mulg with his runes painted (top) vs day-glo powders. (bottom)
Life-Like Effects vs Magic
Is one method better than the other? Not necessarily. When I painted my Fel Caller Shaman, I tried going for a magical effect on his hands instead of fire and while I was at it, used neon orange day-glo for the totem on his back.
As I cover in the article, I didn't like the final look.. it was too bright.. too goofy. I ended up tearing the medium off and painting real fire effects in, which was all kinds of worth it. This is also a good example of how you can simulate strong glow effects without the use of day-glo paints.
So I'd recommend caution when deciding where you'll use these. Sometimes doing a nice blend with regular paints will look all the better.
Mixing Pigments with Mediums
It's also worth noting that day-glo pigments, like any powder, can be mixed with other mediums. If you mix it with matte medium, you can create day-glo paints. If you mix it with sculpting gel or water effects, you can make it look neon too..