Problems with blackening brass

[Desertanimal]

So I’ve read several posts about blackening brass. I’m using Birchwood brass blackener. I prepped the parts by sanding with fine paper, acetone soak, dry. Then in the solution for a few minutes 1-2, rinse with water buff with cloth/paper towel. They look great, I take off the black chalky stuff with the towel and they look like steel. 
I used some blue tape to hold this piece in place to glue and when I took the tape off this is what I got. 🤬

I used a cotton bud and applied more solution and wiped with clean water it turned out well, but I did that on the boat and I was really afraid of getting some on the paint. 
I thought this was more permanent? What am I doing wrong? 
Thanks!

 Chris

 

[barkeater]

The brass blackening agents work as a powder coating on the surface and therefore could be and was pulled off when you stuck tape on. You can help keep the powder coating on by using a sealant. I always give any blackened part an overcoat of Testor's Dulcote (non-shiny) which locks it in. The more you handle blackened parts the greater the risk of removing the coating and I would never use tape on them.

Richard

[Desertanimal]

Thanks for the info! Can’t believe I missed that that I need to coat it afterwards! 
That should make things go a lot better going forward. 

Chris

[CiscoH]

check Blackening Revisited by DVM27 about 3 pages in on this thread.  my personal experience is blackening brass is very frustrating and there are a lot of Mystic Formulas out there.  i sand the brass with 220, rinse in alcohol, and use the same blackener you do.  i’ve had better luck distilling the black at least 10:1 with distilled water (10 parts water to 1 black).  it takes 10-15 minutes to blacken and i turn the pieces over periodically.  i still get small splotches where it doesnt cover, especially on soldered areas where i didnt get all the flux off, but the very dilute blackener seems to stick better than concentrated.  

then i use black paint on any areas that didnt cover.  

[tlevine]

I have the best luck by soaking the parts in warm Sparex, followed by a dip in water and then in a 1:5 solution of Birchwood Casey to water.  I give them several short dips of 15-30 seconds with polishing in between.  Finally, they get a thin coat of Dulcote.  

[Desertanimal]

Looks like I’ll be picking up some Sparex for the next project. Sure sounds like the way to go. 

Chris

[Dr PR]

I have had problems similar to what Chris and others reported - some blotches and the blackening rubs off.

 

I noticed that the parts blacken almost immediately in Birchwood Casey Brass Black diluted 1:1 with water. I have tried leaving them in the bath for 5, 10 and 15 minutes with about the same results. Then I rinse with water 5-10 times and dry the parts. Maybe I should use a minute or less.

 

I normally wash the parts in acetone for a minute or two to remove solder flux, then use rubbing alcohol to remove the acetone, and a final wash with water to remove the alcohol or any remaining water soluble materials. After drying I use the blackening solution.

 

I have also tried etching with mild acetic acid (vinegar) and then rinsing with water. Then the acid/alcohol/water washes. It doesn't seem to make any difference.

[knightyo]

I've had similar frustrations and ended up applying black acrylic paint which ended up looking better than the powder coat.  Next time I have a part to be blackened, it will be a standard prime/paint, which is also far more enjoyable than playing around with caustic chemicals.  

 

Alan

[Desertanimal]

Knight, I’ve thought the same thing. The finish from blackening sure looks good though. As long as I can get it to stay! 
Thanks for all the tips and it’s good to see I’m not alone in my frustration. Somehow that makes it a little better. 🤣

 Chris

[dvm27]

I've had better luck with Brass Black but this is unfortunately no longer available. If any of the part you need to be blackened is soldered then the Sparex works great as a cleaner/etching solution.

[grsjax]

I find that sanding and etching the parts with white vinegar then washing the parts in soapy water, rinsing in clean water followed by dipping in acetone then a rinse in running water as a prep works best for me. Your mileage may vary.

[Desertanimal]

Grsjax, do you then clear coat them? Is the surface permanent without clear coat after this prep?

 Chris

[grsjax]

Haven't tried using clear coat.  I let them age for a couple days before I try to handle them.

[Dr PR]

In another thread someone described using Sparex to prepare brass for blackening. I bought some but haven't used it yet. Most of the blackened parts I have made so far are very small. But for larger parts with large surfaces it seems better reparation is needed to get good even coats.

 

One of the recommendations was to find a small crock pot to heat the Sparex. So I visited out local Good Will store today to see if I could find one. There were about half a dozen, ranging from US$6 to US$9. I got one that holds about a cup to 1 1/2 cups (240 to 360 ml) and it works, heating water to 170F (77C) in about 45 minutes (45 min).

 

I think I will need the Sparex for the more complex machinery on my minesweeper build.

[shipman]

Seems a lot of bother, when a few dabs of paint would be sufficient and permanent.

[tlevine]

I put everything that needs blackening in the Sparex.  Mix up a batch, keep a lid on the pot and plug it in whenever you need it.  Just remember, copper tongs are required to remove anything from it.