I don't know if this is helpful, but I use a stinky ultrasonic cleaning solution in my ultrasonic cleaner for my brass engines and cars. All my "unpainted" brass locomotives and cars had a clear coating on them of some sort, and my ultrasonic cleaner stripped them quite handily...although it took several 30 minute dunkings to get all the old paint off.
Nice thing was that it completely cleaned and de-greased the models too.
I had parts to modify and parts to add to my brass models, so another dip in the cleaner was necessary to remove finger grease, and any flux residue when they were ready to repaint.
No primer since I use Scalecoat paints, which happen to be the best match for UP colors in addition to having that wonderful shiny prototype look that also takes decals so well.
Since I bake my Scalecoat paint in a carefully regulated toaster oven at 150 deg F, it is much more durable than acrylic paint.
Paint thickness will really thicken up detail parts, even without using a primer. I shot my much superdetailed and modified brass UP CA-8 caboose with one coat of Scalecoat II, then brush painted the red end platform ladders & hand rails, along with the red grabs on the sides and ends. When looking at the raw brass model vs the painted model, the grabs, ladders and railings look much skinnier than after they were painted. Part of the problem could be that they're brush painted, but next time I take all that time to get the hand rails, grabs and ladders just the right dimension, I'm going to strip off the uncured base coat color before baking and then mask and spray all of those details with my airbrush rather than use a fine paintbrush on them.
I am sure that will be more to my satisfaction as far as appearance is concerned.
Although prototype paint on real cars and engines can get pretty thick, it's good to keep in mind that a coat of paint that is only .001" thick, on a handrail or grab will increase the diameter by .002" and each additional coat of paint (at a very thin .001" paint thickness) will increase the diameter of cylindrical parts an additional .002"...a noticeable and not-so-good difference! Just to emphasize the problem, adding a nice .001" thick coat of primer, then a .001" thick coat of base color, then a .001" thick coat of grabiron or rail color will increase the diameter of grabs and railings from .006" to .012"...easily doubling the diameter of those parts. So, it's best to use a paint brand that doesn't require a primer, take the paint off of grabs, railings and ladders if they're a different color than the base coat, mask the model & paint the grabs, railings and ladders with an airbrush. If your brass grabs are a much larger diameter than .006", which is usually the case, then the problem is even more pronounced.
Photo (1) - Brass Hallmark "UP Welded Caboose" modified and superdetailed into a proper UP CA-8 Caboose before painting...notice the fine grabs and ladders:
Photo (2) - Brass Hallmark "UP Welded Caboose" after modifications and paint. Notice the much thicker grabs, railings and ladders as compared to the "raw" brass model:
The nice thing about doing this process with Scalecoat II, is that enamel based paints wipe off easily with a brush and paint thinner before they've cured. Not so sure about "wiping off" acrylic based paints...I think you'd have to mask the grabs, railings and ladders you're going to paint a different color than the base color.
Of course, you could simply not worry about it!
Cheerio!
Bob Gilmore
