Many thanks for your kind words people!
Your support is invaluable.
Had a couple more painting sessions. First, let me show a couple of pics to further illustrate the techniques I use.
So, when you cover such detail as a gem with liquid mask, it's inevitable that some of the mask will flow onto the surrounding surface. As a result, when you remove the mask, some of the primer will be showing around the gem:
This is not a problem here because white primer can be easily overpainted with an appropriate shade of red. In the end, no one who doesn't know what to look for would ever notice anything.
Still, this is something to keep in mind if you wish to try this kind of technique out.
Generally, airbrushing works ideal when you can work on a single separate part that has to be mostly one colour. Because of this, painting in sub-assemblies is essential if you want to get the most out of an airbrush. However, sometimes a model is one-piece, and sometimes keeping it in subassemblies is just not practical. In this case, if you still want to airbrush different areas of the model with different colours, liquid mask is what makes it possible. However, you should always keep in mind that
1) applying mask takes time
2) removing it also takes time
3) mask will inevitably leave a line of slightly jagged paint along its border, and you'll need to tidy it up.
As a result, if it's something relatively small, it's usually still quicker to just paint it by hand. The technique that I use with those gems on bikes is a kind of an exception to that - it works for me because I can airbrush any number of those gems in like 5-10 minutes, while hand-blending colours on them would take me hours (due to their large size). Hence despite the extra fuss with the mask, it's still worth it.
With the details on the bike mostly done, I completed all small details on the rider:
Now it was time for the most tedious but also probably the most rewarding stage: black-lining and extreme highlights on the red armour.
First I outlined all armour plates and other details using a thin mix of dark red ink with black and violet airbrush paints. GW recommends doing it with a "recess wash", but using washes at this stage, even if you use them in a controlled manner, is still messy, and besides the end result dramatically lacks contrast. So I use what effectively looks like black-red paint, thinned down and mixed with some acrylic retarder for maximum control, and just paint in thin dark lines into all the recesses.
This picture is not of the best quality, but because of that it showcases the resulting effect really well. When you look at the picture, you don't really see much of those dark lines, but you simply notice that all armour details stand out much more clearly against each other than they did on the previous pictures. I heard some painters calling this "a comic-book style", implying that it looks cartoonish and unrealistic, but I actually find it rather natural and believable.
As a (semi-)side note, there was once an interview with Jes Goodwin (I think it was dedicated to the release of the new Dark Eldar model range somewhere in 2009-2010). In that interview Jes, absolute genious as he is, said one thing that I remember to this day. Can't recreate the exact words, but the idea was that in order to look good, a model doesn't have to be realistic, but it has to be believable and easily recognisable for what it is.
At that moment I realised that this is indeed the principle that governs everything in modelling and painting: things, first and foremost, have to look believable and recognisable. Considering this style of painting Eldar armour, it certainly doesn't look "realistic" in the exact sense of the meaning - but, with all plates clearly defined and standing out, it does confer a very clear feeling of some kind of a protective suite built of rigid plates, and therefore looks like it means business. Or at least that's how I see it, lol
So, black-lining was followed by the first extreme highlight (Wild Rider Red):
... and the second highlight (Fire Dragon Bright).
Even on this washed-out picture you can see that the armour plates now have some definition
What's left with the rider is one more highlight stage on red and highlight on hair. Then the same highlights on red parts of bike, base, and it's done
To be continued