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Blotchy Blackening

Don Case

Don Case

Joined
Jul 10, 2021
Messages
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Location
Vancouver Island
I'm having trouble with blackening. It comes out blotchy. I'm using Birchwood "Super Blue" on copper wire, I couldn't get "Brass Black". To clean the copper I used the pickling solution from silver soldering. The wire is nice and coppery clean when I put it in the Super blue but some parts take the black really well and others don't. I didn't use acetone to clean it as some recommend as I assumed the acid in the pickle would do a good job. Has anyone else had this problem? The copper wire was plastic insulated and I stripped that off. Do you think it's possible that some plastic residue stuck on the wire and the acid didn't clean it? It kind of looks like the parts that didn't take the black are the parts that didn't get heated in the soldering process. Any clues please?DSC04709.JPG
 
Don Case said:
I'm having trouble with blackening. It comes out blotchy. I'm using Birchwood "Super Blue" on copper wire, I couldn't get "Brass Black". To clean the copper I used the pickling solution from silver soldering. The wire is nice and coppery clean when I put it in the Super blue but some parts take the black really well and others don't. I didn't use acetone to clean it as some recommend as I assumed the acid in the pickle would do a good job. Has anyone else had this problem? The copper wire was plastic insulated and I stripped that off. Do you think it's possible that some plastic residue stuck on the wire and the acid didn't clean it? It kind of looks like the parts that didn't take the black are the parts that didn't get heated in the soldering process. Any clues please?View attachment 348764
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Another possibility is that they put something on the copper wire before the insulation. I would try cleaning better for another test. I’ve been able to get brass black from Amazon but I don’t know if there are issues with that for our neighbors to the North.

Jeff
 
Thanks. When I was writing my post it occurred to me that a quick test was in order. I cut a little piece of wire and heated half of it, then cleaned and blackened as usual. I got this

DSC04710.JPG
The blackening took beautifully on the heated side and not at all on the other side. I did a very short blackening treatment. So next I did it again but instead of heating half I cleaned it with acetone. It didn't help at all, the wire didn't blacken anywhere(no picture, imagine a pristine piece of wire :))
So you must be right, there must be some kind of coating put on the wire. I guess I'm going to have to heat the wire before I try to blacken it. It doesn't need much heating, barely enough to start to discolor the metal. Bit of a nuisance but it really makes a difference in the blackening.
 
Thanks YT :) but it looks like the "Super Blue" is working. I just have to heat the wire enough to take the copper shine off and it works great. Now I just have to check and see if the heated wire silver solders as well as the shiny stuff. Right now I'm in the middle of re-heating all my chains and re-blackening them.
 
All done. these are the chains for the main shrouds. Not a hint of copper in the bunch. I'm chuffed. I've been chasing that blotchiness for months. Got it now :). There are some coppery looking lines in the picture but they are shadows. Thanks for the help. Sometimes just the act of posting something triggers a thought.

DSC04711.JPG
 
My understanding of blackening is that copper / brass parts must be ideally clean in order for blackening solution to do a good job. Parts with uneven blackening are ALWAYS not enough cleaned parts.
I had a bigger problem in the past when I used different blackening solution. Parts would blacken all right but black oxide crust would fall off when touched revealing bare copper but this is a completely different story.
 
That was JAX Copper Blackening solution I had these huge problems with. I now threw this crap away and use Birchwood Casey with success.
 
Don, I had a similar problem with blotchy blacking of copper and brass. I didn’t think of heat but took a green scotchbrite pad and “polished” the brass and copper until nice and shiny and everything came out great. So polishing has been my go to method but I may try heat next time and save some elbow grease. Thanks for sharing.
 
"Parts would blacken all right but black oxide crust would fall off when touched revealing bare copper but this is a completely different story."

It's funny you mention that. That's the way these parts would behave if I left it in the blackening solution for a long time trying to get it to work. There would be shiny spots where the blackening didn't take hold and right next to it would be crumbly and flake off.
Now I'm just leaving it in the solution for 2 mins. and it's coming out nice an smooth. It leaves a little black on your fingers if you rub it but then it's fine.
 
Hello Don,
are you diluting the mix, or using it straight from the bottle ? I find a diluted mix works better with distilled water.
 
OlivierF said:
Don, I had a similar problem with blotchy blacking of copper and brass. I didn’t think of heat but took a green scotchbrite pad and “polished” the brass and copper until nice and shiny and everything came out great. So polishing has been my go to method but I may try heat next time and save some elbow grease. Thanks for sharing.
Click to expand...
I was really surprised when the acid pickle didn't clean it enough. Earlier I had actually tried sulfuric acid and it didn't work. At the time I just thought it was the blackening solution failing.
 
Bryian said:
Hello Don,
are you diluting the mix, or using it straight from the bottle ?
Click to expand...
Diluting. I think it's 2:1 water to black but I'm not sure. It's been a while since I mixed it. I read something recently that someone was using a very weak solution and leaving it overnight. They thought they were getting a more durable finish that way. I was considering trying that but this works so well now and only takes two mins. why wait overnight.
 
Don Case said:
"Parts would blacken all right but black oxide crust would fall off when touched revealing bare copper but this is a completely different story."

It's funny you mention that. That's the way these parts would behave if I left it in the blackening solution for a long time trying to get it to work. There would be shiny spots where the blackening didn't take hold and right next to it would be crumbly and flake off.
Now I'm just leaving it in the solution for 2 mins. and it's coming out nice a smooth. It leaves a little black on your fingers if you rub it but then it's fine.
Click to expand...
I found that buffing the blackened pieces removes the dust and leaves a nice patina. I took a cheap 3/4” nylon paint brush and cut about half the bristles off making it a little stiffer. After rinsing and drying the pieces I brush the dust off. No more mess on my fingers.
 
OlivierF said:
I found that buffing the blackened pieces removes the dust and leaves a nice patina. I took a cheap 3/4” nylon paint brush and cut about half the bristles off making it a little stiffer. After rinsing and drying the pieces I brush the dust off. No more mess on my fingers.
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I like that idea. Do you just dump the part on a cloth and buff them there? I've just been wiping them off with my fingers but I have been worried about transferring the dust to the ship's nice white planking. Been washing my hands a lot :)
 
Don Case said:
I like that idea. Do you just dump the part on a cloth and buff them there? I've just been wiping them off with my fingers but I have been worried about transferring the dust to the ship's nice white planking. Been washing my hands a lot :)
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Yes sir. I usually use a blue paper towel (Costco disposable shop towels) but have also used microfiber towels to dry the rinsed parts. once dry I just take my brush and buff the parts. It really takes no effort to get the dust off.
 
Looks like you've solved your problem but one thing that occurred to me was whether the surface could still have been slightly acidic when you tried blackening. When we used to get stainless steel pickled it was always "pickle and passivate", the passivation being an alkaline solution to neutralize any acidic residue. I THINK the cold bluing solutions are alkaline, but only did a rudimentary check on that this morning. Just my impressions. Interesting topic and discussion.
 
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When I blacken I set up three tubs. Pickle, water and blackener so everything gets rinsed between pickle and blackener. I also use wooden tweezers to avoid contamination. Maybe a little bi-carb in the water would be a good idea:). I always thought the blackener was acidic but I have no idea where I got that from. I could be wrong.
 
Hi, interesting discussion. If you would like a chemical explanation: plastic coated copper wire has been treated with an antioxidant/brightening chemical which stops the surface of the copper oxidising and turning black during the manufacturing process. That is why when you strip back wire the copper is always nice and shiny. The coating is chemically bonded to the surface which is why it is difficult to remove and prevents the blackening solution working because that is an oxidation process. Using a stronger acid pickling solution with anionic surfactants and some warming will work. It is easier to just buy some uncoated copper wire and clean it with a mild acid detergent. I did some experiments with different cleaning solutions to see what works best and I found that Turtlewax alloy wheel cleaning solution does a really good job at removing grease and tarnish from brass, copper and white metal and they then blacken very evenly!
 
Thanks for that explanation. Unfortunately I worked for the telephone company so I have a rather large collection of plastic insulated copper wire. So I won't be buying any copper in this lifetime :) Heating it has worked well. I thought the heating would oxidize it and make silver soldering difficult but that hasn't proven to be the case. Heat, solder, pickle and blacken. Seems to be working a treat.
 
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