Airbrushing: Acrylics and Masking

[James Costello]

I began airbrushing my SD70M project over the weekend and am not satisfied with my results so far. I was using an Aztek airbrush and Polly Scale paints and had been following the guide on Trainboard http://www.trainboard.com/grapevine/showthread.php?t=77908 on how to do so. This was my first experiences with airbrushing a loco shell with Polly Scale and masking/painting multiple colors.

I am trying to paint the EMD demonstrator scheme on the SD70Ms - red/silver/grey as shown:
http://locophotos.com/Search.php?SearchRoadID=849&SearchModel=EMD+SD70M&Search=Search
I had read that masking over silver is often problematic, so I decided to leave the silver to last and go red, grey and silver.

After preparing the shell, I painted the red on Friday and on Saturday, roughly masked off the red. I masked the red further down than needed so that I could ensure I had enough coverage of the red for when I masked it properly for the silver. In his thread, Jim recommended using the Aztek white nozzle for Polly Scale, but I had problems with blockages when painting the red, despite thinning it with water ~25%, so I used the same sized "general purpose" grey nozzle and had no problems with paint flow. I was pretty happy with the red coat but had a little bleed through and overspray with the grey that was dissappointing, but could be fixed with a light touch up of the red.

Here's a couple of photos showing progress at this stage:





Yesterday's application of the silver is where the heartache began. During the masking process, I had questioned how successful masking the red off was going to be - the radiator screens on the side posed a problem to mask of a thin line for the red towards the rear of the long hood. The angled cutouts beside the "Electro-Motive" was going to be challenging either way. The cab had its own challenges: the thin layer of red across the front of the nose and the curved grey areas. I masked off the cab first - both the red and the grey. The curved area was free-handed onto tape and cut out. I used both Tamiya's thin masking tape and regular masking tape. I did the grey on the long hood and matched it up with the cab but decided not to mask the red - it had to be touched up anyway and getting it right under radiator was going to be tough. I wanted to see if this method was going to be successful too.

Here's the result:











So yeah, obviously not too happy with how it looks. The existing masked separation line is still visible under the silver and I've got paint build up along the masked edge - mainly on the long hood, but also on the cab. I sprayed all coats around 15-20 PSI as recommended by Jim. I think I've rushed the thin coats and put too much paint on during each pass, probably as I was finding it hard to notice the effect of each pass. There's some bleed through of the silver onto the grey too, despite burring the edges down with a toothpick. This seems to be focused between the long hood engine doors. The curved section on the nose is ok and would be passable, but I think I'll try to make a pattern in styrene and use it as a template (Rob's front on nose photo, which I only just found today despite many searches over the years, should be a good guide for this and will hopefully give me a better shape).

I think I'll have to strip these shells and start again. Unless I put a primer layer down to cover the separation line and than apply the silver, but I don't want to end up with too much paint on the shell.

So, apart from more patience during the spraying process and keeping the passes light to avoid paint build-up, what else can I do to improve this process?

Should I start with the silver and mask it off, spraying the red and grey on each side of that?
Should I pre-spray these colours with silver to prevent any possible bleed through under the tape?

Does anyone who sprays Polly Scale regularly have anyother suggestions?

Thanks

[central.vermont]

James,

One thing I do to prevent paint bleed under the tape is too
spray dullcoat on after I have thoroughly burnished all the
edges down. Also many many light coats will keep the paint
edge to a minimum. What actually happens is that the paint
while it is wet will form a fillet at the edge of the tape. It takes
some practice and patience to get it right. Frustrating as it may
be. 

Hope this helps some.
Jon

[Guilford Guy]

What tape were you using? Painters tape has a fairly rough edge. I'd recommend using Tamiya's tape. Tamiya tape has a straight edge and doesn't pull on the underlying paint. Hitting the loco with a clear coat after masking helps seal the edge so it won't bleed through. Lastly I'd have to agree with Jon on the many light coats. When painting, coats that barely cover underlying color in the beginning give a smoother coat and will dry very quickly so there is little to no bleeding.

[GaryHinshaw]

What a drag.  It looks like the basic problem is the paint is going on too wet and heavy, but it's still not covering very well.  I have had very mixed results with silver colors with some of them being almost worthless at covering.  I've had pretty good luck with Polly Scale Aluminum.  But definitely use lots of thin coats and angle the spray slightly away from the tape joint rather than into it.  As Jon notes, I think spraying a light clear coat could help too.

You might want to practice on a scrap shell, or a piece of styrene first...

Cheers,
Gary

P.S. I should add that I'm a rank amateur at multi-color paint jobs... so my advice is only worth what you paid for it. 

[Chris333]

I didn't have any luck spraying silver water based paint. Ended up using solvent based. Silver is a weird color.

[diezmon]

make sure you don't use the factory edge of the tape.  I always lay it on a piece of glass and cut a new straight edge with a razor.

Then, after each masking, I spray a light coat of the previous color before the new color.  That seals the tape edge, and if there is bleeding, it's the same color.   You can also just spray clear, as already suggested.

Also, I use a toothpick to burnish the tape down really well into the details.

[diburning]

The edge of the tape is exposed to everything, you hands, the dust in the air, the ground if you drop it, etc.  The factory edge will not be as tacky as the center of the tape, so it will cause bleeding by not sticking as well to the model.

[shamoo737]

One technique I use is to paint away from the tape edges so the paint doesn't accumulate at the edges.

[noblerot]

I would also like to mention how important it is to burnish the tape edges before painting. I use a plastic burnishing tool to get the edges tight and always get crisp edges with light coats

[mcjaco]

Then, after each masking, I spray a light coat of the previous color before the new color.  That seals the tape edge, and if there is bleeding, it's the same color.   You can also just spray clear, as already suggested.

Also, I use a toothpick to burnish the tape down really well into the details.

I do the same technique.  It's hasn't backfired on me yet.  Any bleeding, if there is any, is minimal and can be touched up with a small brush.

[inkaneer]

You guys have hit on the very reasons why I shy away from paint schemes with muti-colors in them.  Unless, of course I buy them that way from the manufacturer.  But even there I notice some obvious screwups but nothing on the scale that I am capable of.  That being said I am a whiz at painting undecorated open hopper cars.  Black, red or brown don't phase me one bit!

[James Costello]

Just so everyone knows, it all turned out fine in the end:



Some good tips here in this thread though. Light coats are important!

[noblerot]

That turned out really nice. Good looking paint scheme.