How to blacken brass

In this case you have to paint it. Try using a good enamel paint finish doesn't matter.

Then spray matte clear.

Johnny, you might try soaking the pieces in an acid bath before trying the JAX blackener. Purple Power is a great degreaser, but brass really requires a bit of etching to hold the black and PP doesn't really do that so well. Try soaking the part in a diluted muriatic acid or straight white vinegar for a few hours before trying the JAX again. The acids will etch and pit the surface of the brass at a microscopic level, which gives it a far more aggressive hold. 

Brass parts are one area where you need a decent primer coat. Simply applying a coat of flat black paint won't cut it. As you found, it'll scratch off very easily. 

Scuff the surface a little with steel wool or a scotchbrite scourer (this step is even more important if the brass has tarnished), then wash in soapy water to remove grease/skin oils. 

There are some hobby grade metal primers available but you should be able to get by with a decent lacquer based primer like Tamiya Liquid Surface Primer or Mr Surfacer. Once cured, it should give you a nice solid base for your top colour.

I have not used that particular blackener (I use Casey's brass blackener myself).  I have long had similar problems though.  The brass must be scrupulously clean.  I do not like to use any detergent or soap, however.  I find getting all soap film off  is as much of a challenge as getting the grease off.  I use a lacquer thinner to clean brass now- no residue.  There is also an auto body product- degreaser and dewaxer that works well as a last resort, but it is more expensive than lacquer thinner.

Finally I am careful when done blackening.  I rinse the part(s) off with water, being careful to not touch them during the rinse, and not run water into the tub too aggressively so parts do not get bumped around.  I carefully pick them out of tub and lay on a kleenex till dry.  The coatings are fragile, so I handle them with care, and do not rub them with anything.

Post drew my attention because I just finished an M4 high speed tractor that used fine brass colored chain for the winch. Naturally I wanted to make it anything other than bright gold in color but even highly thinned paint would not stick and unless it was thinned to almost water like all it would do is plug the teeny link opening up.

Thanks everyone for the great ideas. Next time I'll etch or sand the brass first.

The JAX blackener is weird stuff. If you let the brass parts soak in the blackener a black crust builds up on the brass which falls off when the part is rinsed in water. The best way to use JAX is to dip the brass part in the JAX and remove it when it turns black. This can be done multiple times to get a dark black finish. However, it is still a fragile finish.

Here's my puzzlement.

The fact that your MG barrels are brass is solely because whatever co. is making them chose to cast them in brass, probably by lost-wax.

But the real things aren't brass, they are either painted or blued.

So goal 1 is to get any trace of brass hidden.

Just like photo etched parts, clean them thoroughly, prime them, then paint them.

And go easy on the thickness of paint. I prime with Tamiya white and then go with enamels or acrylic. Unlike most smart folks, I like a primer thats not the same color as the finish. It makes it much easier to judge coverage of the color. Also, my understanding is that color paint is formulated to look correct over white.

Bill

JohnnyK

The JAX blackener is weird stuff. If you let the brass parts soak in the blackener a black crust builds up on the brass which falls off when the part is rinsed in water. The best way to use JAX is to dip the brass part in the JAX and remove it when it turns black. This can be done multiple times to get a dark black finish. However, it is still a fragile finish.

 

If you're getting a crusty layer or an uneven brownish-grey color in the brass, you may also want to gently warm the JAX solution before you use it. That will help prevent the salt crust.

Also, consider using a paintbrush to apply the stuff and build it up slowly until you're satisfied with the finish. It takes a little longer than immersion, but for whatever reason, the brush just seems to work better. 

The finish is always going to be a bit fragile. Most of the time that I reach for the stuff, I will be buffing the metal latter on with a Scotch Brite wheel to remove most of the black to give an antiqued patina to brass or pewter. To protect that finish from scratches when you handle it, you're going to have to give it a clear coat. HTH.

GMorrison

Here's my puzzlement.

The fact that your MG barrels are brass is solely because whatever co. is making them chose to cast them in brass, probably by lost-wax.

But the real things aren't brass, they are either painted or blued.

So goal 1 is to get any trace of brass hidden.

Just like photo etched parts, clean them thoroughly, prime them, then paint them.

And go easy on the thickness of paint. I prime with Tamiya white and then go with enamels or acrylic. Unlike most smart folks, I like a primer thats not the same color as the finish. It makes it much easier to judge coverage of the color. Also, my understanding is that color paint is formulated to look correct over white.

 

Bill

 

While brass was used in a few very small guns, larger (cannons) were either bronze or iron.  The iron ones were always painted, and many bronze ones were also.  Bronze is not the same color as brass.  It is closer to a copper color.  I paint bronze cannons with copper first, overcoat with a very thin coat of brown, then a very light wash of olive drab.

BTW, if you carefully monitor brass in blackening solution, and stop it before it just turns completely black, it can look a lot like painted iron.

Hi;

 Somehow my post got mislaid. So here goes again. Try a product made for Stained Glass Hobbyists. I have NEVER had problems with this stuff rubbing off or flaking.