I've made a small discovery. Well, "discovery" is the wrong word, because it's actually completely logical, but let's stick with that word.
I've been trying to paint this mini Rubik's cube for years (literally!). It's been a pain cleaning it's surface of whatever dirty glue they used to keep the stickers on and when I finally got it clean enough, no paint would stick to it. In fact, the paint just peels of again.
Anyhow. Once every few months, I manage to build up the courage to paint ONE side, then let dry and treat it with multiple layers of "Future" (Currently: Pledge's "Floor care - Tile & Vinyl Floor finish"). It's the only product so far that keeps the paint on the plastic.
So, what did you discover !?
I had just painted the third side bright red. After removing the masking tape, I saw some of the red paint had creeped under the tape and stained the blue side. I would normally clean up with thinner, but couldn't find the thinner right away, so opted for Vallejo's Airbrush cleaner. I though it'd be safe, since the blue was already under multiple layers of Future.
Guess again! The cleaner ate the future AND the blue paint. Now, this shouldn't be THAT surprising, since Future is also an acrylic and therefor a bad protection against an acrylic product cleaner.
It immediately made me think of a technique I recently read, namely Mike Rinaldi's alternative for the hairspray technique (or chipping fluid). He calls it "Lacquer thinner dry-brushing".
Basically, once you have multiple layers of paint on your model (like camouflage on top of red primer, or just several different shades of Olive Drab), you wet a fine brush with lacquer thinner (only slightly moist) and softly start working on the surface. Little flakes (let's call them "chips"?) of the paint will start to come loose, just like when you're using the hairspray technique, except that this does not depend on any intermediate product to be applied beforehand.
In my case, I went all the way to he plastic of course - which isn't how this technique is intended - but I'm considering giving this one a go in favour of my not-so-successful attempts at the hairspray technique so far. (mostly undocumented yet, so you haven't read much about it)
An in-between layer (e.g. varnish) that does not respond to the cleaner might solve the problem of "going to deep", but Mister Rinaldi is no fan of varnishes. I am however, but it's safe to say his experience and skill outweighs mine by a huge factor.
I'd say "stay tuned for test results", but at the rate I'm currently going, that'll be sometime next year.
Stay tuned anyway, I'm intending to actually finish a few projects rather soon(-ish).