Author Topic: Spray painting brass  (Read 1132 times)

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Scottl

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Spray painting brass
« on: April 05, 2014, 04:04:38 PM »
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I've spent quite a bit of time searching here and elsewhere to get some sense of the best approaches to spray painting brass on a model.  In my case, it will be etched brass bridge sub assemblies.  I picked up some paints over the last week to test and tried on some scrap brass outside today.  The paint was room temperature, but the outside air temperature was about 3-4degC, so I know it was on the cold side.  The brass was washed and scrubbed with an old toothbrush in warm soapy water, rinsed, and thoroughly dried prior to paint application.

I tried both Krylon camouflage black (solvent based) and Liquitex Cadmium Orange (water based) and found they did not give a very even coat on the bare brass.  They tended to "bead" up a bit rather than level into a smooth surface, although the Krylon did level a bit better.  I thoroughly mixed them by shaking for several minutes before application.

I am a bit underwhelmed by these initial results, so I am left wondering- what is the best way to spray paint brass like this?  A few things I picked up from TRW threads:

1.  Wash the metal, some suggest using just soap and water, others Bestine, others acid wash with vinegar.
2.  Some roughen the metal up with sand blasting prior to painting.
3.  Some seem to use automotive primer first.  I am sensitive to building up too much paint which might obscure details.  My tests today showed no real obscuration of rivets, so perhaps a few coats is not a problem.

Any tried and true methods?  Things to avoid?  Advice to leave the rattle cans on the shelf and airbrush? Any particular types/brands that people have used with success  (or otherwise)?

Thanks for your comments.





Kisatchie

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Re: Spray painting brass
« Reply #1 on: April 05, 2014, 04:59:35 PM »
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You should give Scalecoat I a try (NOT Scalecoat II). It's extremely suitable for brass, goes on super thin with an airbrush, and is almost impossible to get off once it dries, especially if you bake it on according to instructions.

Note - I wouldn't spray it in such low temps, though.


Hmm... yeah, Scalecoat II
is for plastics...


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Scottl

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Re: Spray painting brass
« Reply #2 on: April 05, 2014, 05:20:59 PM »
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I'm pretty sure I can't bake the paint, in part because there is some styrene in model, but also because it was assembled with CA.


peteski

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Re: Spray painting brass
« Reply #3 on: April 05, 2014, 05:26:13 PM »
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I would use primer first. As dark of a primer as you can find for the black and white primer for the orange.

For bare metal I usually get a can of self-etching primer at an automotive body supply shop.  But for N scale work, I decant it and spray it through an airbrush. That way I have much better control of the paint volume and direction. That would make spraying all the crevices in a bridge easier (without flooding all the surrounding areas with too much paint).
« Last Edit: April 05, 2014, 05:27:49 PM by peteski »
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Kisatchie

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Re: Spray painting brass
« Reply #4 on: April 05, 2014, 05:32:42 PM »
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I'm pretty sure I can't bake the paint, in part because there is some styrene in model, but also because it was assembled with CA.

What I did instead of actually baking my brass in an oven... well, I lived in New Orleans where summers get pretty hot. I painted the brass in July and let it dry in the closed-up garage for a couple of days. Poor man's baking.


Hmm... I'll have to try
that with some termites...


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Scottl

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Re: Spray painting brass
« Reply #5 on: April 05, 2014, 05:55:58 PM »
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That is a good idea.  I could put it in my SUV to cure on a hot day- it gets well over 50degC in there...

I like the idea of the etching primer.  I might give that a try.

Temperature definitely played a role in my early results.  I tried a bit of the Krylon black in my paint booth and it gave a very smooth finish.  I still think some primer is a good idea.

peteski

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Re: Spray painting brass
« Reply #6 on: April 05, 2014, 06:04:04 PM »
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As far as baking goes, Kiz is onto something. I put my painted models (automitive, railroad, etc.) in a food dehydrator all the time.  It really speeds up drying time (and I'm sure it makes the paint cure harder).  Mine stays around 100-120 deg. F.

If your bridge assemblies are small enough, investing in a food dehydrator might be a good idea.  It works year-around.  :) Just make sure you either get one that is temperature controlled, or one which doesn't get too hot (for me 120 deg. F is pretty much as high as I dare to go).
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CoalPorter

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Re: Spray painting brass
« Reply #7 on: April 06, 2014, 03:09:10 PM »
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For the most part, I have found metal to paint way better than plastic.
I too second using Scalecoat I (made for metal) applied with an airbrush.
I would avoid using spray cans for fine model work.
If you are having problems with beading-up, then your metal may already
have some clear coat finish on it that needs to be removed.

I have painted several brass tank cars from Pecos River, and they really came
out TOO GOOD for model railroading - it looked more like the finish on a Bentley,
and I was really amazed and stocked at the quality compared to painting a plastic model.
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robert3985

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Re: Spray painting brass
« Reply #8 on: April 07, 2014, 03:38:50 AM »
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This may be a little late as your other post indicates you've already painted your project.  However, I'm giving one more vote for Scalecoat I.  I use it for all my brass UP cabooses and engines without primer and it works GREAT!  I always bake the pieces too, but just letting the pieces set for a while ( a few days)  until the aroma goes away will do just as well.  I find the finishes to be opaque (UP Armour Yellow NEEDS to be opaque) and extremely durable.

Just sayin'....

peteski

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Re: Spray painting brass
« Reply #9 on: April 08, 2014, 01:59:17 AM »
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Scott mentioned that the bridge has styrene parts and CA glue. Scalecoat I might attack those (if unprimed).
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Ike the BN Freak

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Re: Spray painting brass
« Reply #10 on: April 08, 2014, 06:00:53 AM »
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I would use primer first. As dark of a primer as you can find for the black and white primer for the orange.

For bare metal I usually get a can of self-etching primer at an automotive body supply shop.  But for N scale work, I decant it and spray it through an airbrush. That way I have much better control of the paint volume and direction. That would make spraying all the crevices in a bridge easier (without flooding all the surrounding areas with too much paint).

Got a bunch of brass car sides to do the BN Business train, if I use the self-etching primer, I should be able to use any paint after the primer, right?

DKS

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Re: Spray painting brass
« Reply #11 on: April 08, 2014, 07:41:53 AM »
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FWIW, when I paint brass models, I start with a vinegar bath to etch the brass a bit. Then I will prime before applying a topcoat. I most often prime with a rattle-can paint such as Rustoleum. My brass models frequently have styrene parts mixed in, but I've never had an issue of the primer attacking the styrene. For the topcoat, I've used a wide variety of paints, from acrylics to enamels, and they all work fine. I try as best as possible to let the model sit undisturbed for several days, so that the paints are fully dry, before handling the model, weathering, decaling, etc.
« Last Edit: April 08, 2014, 07:44:55 AM by David K. Smith »
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Scottl

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Re: Spray painting brass
« Reply #12 on: April 08, 2014, 07:52:33 AM »
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In the end, I first washed the parts with soap and warm water and a light scrubbing with a toothbrush, followed by a dip in 25% acetic acid to etch the brass, and then the primer coat, which was a mixture of Polyscale flat black and SP lettering gray.  It worked very well, and given that I had to make sure I was getting the paint into the nooks and crannies of a complex structure, I opted for an airbrush rather than a spray can to maximize control.

I will probably decant some of the Liquitex spray paint to try air brushing it.  I like the paint, but I don't want to take a chance with laying too thick of a coat (which seems to be a personal habit with spray cans).

My concern about Scalecoat was primarily availability.  The paint section of my LHS looks like a grocery store before a hurricane.