The Model Boatyard - Blackening Brass

I used to have quite a bit of trouble with blackening brass. Seems like no matter how well I tried cleaning the brass before blackening, the black would still rub or flake off. Recently, my brother gave me a great tip for cleaning the brass before blackening that really works. So here is the entire procedure I use.

Supplies

You'll need two chemicals - muriatic acid and brass blackener. Muriatic acid should be available at most any hardware store. It's really hydrochloric acid and is used for cleaning concrete among other things. This stuff can be dangerous, so read the safety precautions on the package! Your safety is in your hands, not mine. I dilute the acid from the bottle about 50/50 with plain old tap water and store it in a well-marked plastic container.

There are at least 3 brands of brass blackener. I've tried two - Blacken-It and Birchwood Casey Brass Black.(Hoppes is the third I'm aware of but haven't tried it.) Both work well although they give slightly different results. Blacken-It seems to have a bit more of a matte finish and a slightly different color. At the moment, I'm using the Birchwood Casey.

Brass blackening chemicals Blacken-It is available from Micro Mark (part number 60864) and can often be found in hobby stores - especially those that cater to the model train enthusiast. Birchwood Casey is available from gun dealers. The cheapest online source I found is http://www.outdoorsuperstore.com (no endorsement here - I've never ordered anything from them). Both products are about the same price.

I recommend diluting either product. I've heard of some modelers diluting Blacken-It as much as 10-to-1. That seems a bit much to me. I prefer 50/50. Same with the Caseys. Diluting slows down the blackening process a bit and makes it more controllable. As with the muriatic acid, I store the diluted mixture in a small plastic container with a tight-fitting lid. You will use both of them over and over rather than throwing them out with each use, so you want something that will be good for storage.

Technique

When I need to blacken a part, I start by dunking it into the acid. You can let it sit in there as long as you want. My brother lets his parts sit overnight. I'm less patient, so I let mine sit about 10 minutes. That seems to be enough time. I stir the part around a few times just to make sure the acid gets to all of it. This is especially important if you're doing multiple parts at the same time. I use a wooden stick to stir the parts.

When you think it's been in the acid long enough (or you happen to remember it) remove the part from the acid with a pair of tweezers rather than your fingers and rinse well with tap water. Sometimes, I just pour the acid into another container and rinse the parts right in the original container. Then I toss the part into the brass blackener and watch it. You'll want to stir it around while it's in there (I use a wooden stick for this). Again - especially important if you're doing multiple parts. It shouldn't take too long to blacken nicely. When it looks good and black, remove the part and rinse well with water. Again, probably best not to use your fingers for this but you may not want to use metal tweezers - they can turn black too. Allow the part to dry on a paper towel. When the part is dry, you will likely notice a black residue on it. Buff this off with an old t-shirt or other soft cloth.

Brass parts before blackening In these two images, you can see the brass parts before and after blackening. Note that I soldered the ring closed using lead-free silver solder (Stay Brite from Micro Mark). I deliberately didn't do a great job of soldering. I wanted to see if the solder would blacken so I left a lot of excess solder on the part. (The solder was much brighter than it appears in the photo.) As shown in the photo below, this small bit of solder blackened just fine. I have had some problems blackening solder in the past but, as I say, I had problems with the brass too. Your mileage may vary.

The bright highlights on the blackened parts in this photo are not indicative of incomplete blackening but simply highlights from the lamp used to light the part for photographing it. Although it's hard to tell here, the parts have a slight sheen to them.

I'd say these parts look pretty much like black iron - wouldn't you?

If you happen to scratch the part down to brass while you're installing it, you can sometimes touch it up with a Sharpie (black permanent marker).