The Gem paints are a pain in the arse. I got a pretty decent effect painting a Knight-Azyros cherry red, and I will never try to do it again because the same effect can now be done using Contrast paints:
Leadbelcher > Drybrush Runefang > Contrast Paint of your choice.
I have to say, however, that I couldn't get it the way I wanted it, and have given up doing that.
You can do the same thing with Glazes. It's basically the same result.
Also be aware that GW produces gloss shades now. They have their place. I've never used a gloss wash in my life. But I suppose this would be a good time.
A friend of mine used iridescent paint to paint a Wraithknight. It didn't look very good.Specifically: if you’ve ever used an iridescent/opalescent paint, do you have a favorite brand/type and how has it worked for you?