Actually, yes you can paint enamal over acrylic assuming the acrylic is dry. The only problem would come from the thinner used with the enamel. If it's mineral spirits you'll be fine...lacquer thinner however may soften the acrylic if the concentration is too high. Also it depends on how you intend to apply the overcoat. If you're hand brushing you have a better chance of harming the lower layer of paint due to the higher concentration of paint and solvent plus the abrasive action of the brush. If you're spraying with an airbrush it's much easier and safer.
Now, going the other direction...you have to be certain that the enamel layer is fully cured before applying acrylic over it. Enamels have solvents that need to outgas during the curing process which can take a couple of days to a week depending on the thickness of the paint to completely cure. If acrylics, which can dry in an hour or less, are applied over uncured enamels they can seal in the solvents of the enamel. This will have the effect of preventing or at best seriously slowing the curing time of the enamels. Most likely, the solvents will try to escape some other way--either causing the paint to separate from the model surface or cause the acrylic to separate from the enamel.
.....or cause the acrylic to separate from the enamel.
That's pretty much the way I've always seen it. What you basically have is oil and water, and we all know they don't mix. I'm an enamel painter, and yeah, you have to wait awhile for that enamel to cure before you hit it with acrylic (I usually give it 2 days). I use acrylics mainly for washes. What I've done in the past is bought a can of matte "acrylic" clear coat and sprayed my model (way after all the enamel has cured), then when I come in with acrylic washes, the model handles it really well.
Enamel needs longer than that to cure.
There is a difference between being dry and actual curing.
Enamel will be dry and can be handled after a day or two.
But it takes a week or two for it to fully cure to the point that all the solvents have outgassed.
Just like acrylic will be dry to the touch in an hour or two. But needs at least a couple days to be fully set to where you can clear-coat over it.
About the light.
Almost any heat source will speed drying. So putting parts near any type of incandescant bulb will speed things up. Just be sure you don't melt the parts.
Yeah, acrylic washes shouldn't be too much of a problem as they aren't thick enough to impeed the outgassing that much.
But I can attest to the problem. I have experienced it first hand.
Several years ago, I was in a rush to wrap up a contest entry for WF.
Clearcoated a kit only a couple of days after putting some enamel on it.
No problem. Kit looked good.
Fast forward a couple of years. Suddenly, the kit that looked so good on my shelf suddenly started developing white spots!
Everywhere that I had used the enamel before the clear coat started fogging up.
Looked like when you get glue on a clear windshield on a car kit.
And it only happened where I had used the enamels shortly before clearcoating.
Everything else was still good.
Oh man, that sucks. Maybe I've been lucky because I use severely watered down washes. Never thick or substantial coats of acrylic. Lately, I've been using lots of pastel pencils. Occasionally I have problems with them running after a spray of dull coat. Now I gotta figure that one out....
LOL, Ross, so true. Sometimes they disappear and sometimes they go darker. Weird, weird, weird. I was thinking about the dullcoat bottle w/brush, but then I was worried about smearing the pastel around. On this vampire I wanted to brush gloss onto his eyes, but I used a black pastel for his slits and was worried the gloss would turn his eyes into a nightmare.
The demos I have seen at WF all had the person demonstrating spraying dulcote very lightly from about an arm's length away.
They all said that any closer or heavier and you would run into problems with the spray actually blowing the pastels off the kit.
After a couple of light coats from that far away you can go a little heavier and closer.
But the first ones kind of lock it into place and keep if from getting blown off the kit.