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Old 21st Mar 2018, 1:37 pm   #1
The Philpott
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Default Attacking verdigris on complex items?

I have some complications with this case of Avo green death, the battery contacts are (presumably) nickel plated bronze, all the rivets are brass, the fuse holders are silver plated brass and there are odd blobs of solder on the tags. The board is bakelite.

I think that pretty much any aggressive solution i plop these assemblies in is going to eat the brass rivets first and leave the nobler metals alone.. also traces are likely to get trapped inbetween the battery contacts and the board and re-start the corrosion as soon as a bit of moisture condenses. The back of the board is slightly c/sunk where the rivets are installed, so it might be feasible to drill the battery contacts off and treat them separately, then refit very small nuts and c/s set screws in place instead of rivets. (a bit of solder might help lock them in place..?) The rivets don't actually form part of the electrical continuity, which helps. Does anyone have any thoughts on this?

Dave
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Old 21st Mar 2018, 1:51 pm   #2
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Default Re: Attacking verdigris on complex items?

Good question.

Would mechanical cleaning (fibreglass brush, emery paper, metal polish etc.) suffice?

I agree that those rivets would have to come off if they were part of the electrical circuit, so it's rather nice that they're not.

Hopefully, the damage is superficial and hasn't weakened anything. I had some 1930s clock hands recently which looked like this, but which crumbled to dust without much provocation.

Please keep us informed of your progress, Dave.

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Old 21st Mar 2018, 2:24 pm   #3
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Default Re: Attacking verdigris on complex items?

Thanks Nick, i will certainly update as i am determined to see if i can kill it - the one nearest the camera was in my scruffy garage Avo and the dampness made the corruption migrate onto (the brass end of) my homemade lithium cell cassette. I knew it was contagious but i didn't think it would have to be quarantined quite this quickly!

Dave
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Old 21st Mar 2018, 2:39 pm   #4
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Default Re: Attacking verdigris on complex items?

The green corrosion is usually taken to be a single compound though it is more likely to be a range of stoichiometric and non-stoichiometric compounds. Some of these will be more soluble in water than others. I would go for Nicks idea of a very mild abrasive with warm tap water and a little detergent. A drop or two of washing up liquid would do here. When you have removed all you can in this way you could try a gentle chemical approach with anything that's left. I would try a dilute solution of a weak acid. I would try citric acid. Some experimentation might be necessary here. Start with a very dilute solution increasing the concentration until you just get a reaction. Continue with this until you are happy with the outcome without causing further damage. Wash everything with tap water then wash again in deionised water then dry thoroughly. A very light coating of silicon grease might protect for the future. Good luck with whatever you decide to try.

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Old 21st Mar 2018, 3:39 pm   #5
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Default Re: Attacking verdigris on complex items?

I assumed that this was partially caused by something given off by the battery, interesting to hear that you think it's entirely down to the damp atmosphere.

Migration? How does that work with verdigris?

Cheers,

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Old 21st Mar 2018, 5:09 pm   #6
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Default Re: Attacking verdigris on complex items?

Oh i see- yes it was entirely caused by exudate from the 10 cell battery, but out of the two battery holders pictured, one was then used/stored in damp conditions, which seemed to reactivate/accelerate the corrosion. The brass spacer on the end of my homemade battery then developed a brown/black patch (dezincification probably) but only where it was touching the contact affected by verdigris.

I have now drilled the two worst contacts out (2mm bit too small, 2.5mm too large, so used 2.5mm and just weakened the head of the rivet enough to pull the remainder out) and had them in a bath in 1:1 lemon juice/tap water for half an hour. Could be a combination of various things like hydroxide/carbonate/chloride, as some of the green was very tough and had to be abraded away afterwards with a (rounded) blade. The Nickel remains quite shiny and where the Copper is exposed it has gone very dark- as if the Cu had become sacrificial anode (or then again it could just be dezincing.)

I will now rinse them and hang them in the potting shed for observation before deeming them OK.

The fuse holders for attention next- one of them can be removed permanently if need be as it only caters for a spare fuse. I certainly can't replace their rivet/s with set screws and nuts though, as there wouldn't be room to install the fuse.

Dave
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Old 21st Mar 2018, 5:11 pm   #7
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Default Re: Attacking verdigris on complex items?

One technique used by camera restorers for very delicate parts is a long (hours and hours) go in an ultrasonic cleaner .
 
Old 21st Mar 2018, 5:19 pm   #8
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Default Re: Attacking verdigris on complex items?

Bizarrely the camera has picked out green bits that were not readily visible with the naked eye! It's an improvement though.

I never invested in an ultrasonic cleaner-- unfortunately..
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Old 21st Mar 2018, 6:20 pm   #9
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Default Re: Attacking verdigris on complex items?

I would totally avoid using washing up liquid on radio/electronics parts; it is full of salt and the chloride ion is the 'Great Satan' of corrosion. Once it has been adsorbed on a metal surface, getting it all off is hard to do. Of course, chloride is also present in sweat.

Many industrial cleaning procedures include a final stage of rinsing in alcohol as a means of removing water and allowing fast drying, so discouraging any electrochemical activity from getting started.

I'm not sure whether the use of silicones on electrical equipment is a good idea; I'd go with Vaseline.

B
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Old 21st Mar 2018, 6:55 pm   #10
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Default Re: Attacking verdigris on complex items?

A 50:50 mix of white vinegar and lemon juice seems in my experience to be pretty effective and not too aggressive.
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Old 21st Mar 2018, 7:38 pm   #11
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Default Re: Attacking verdigris on complex items?

I just removed and soaked the other 2 contacts in (pure) lemon juice this time, for twice as long (ie an hour) and the difference was ALL the grot came off and the lemon juice went pale green. No effort involved.

Fair play, this is better than I expected. I note that the more nickel plating that is intact the better the result. They are going into distilled water now- maybe overnight.
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Old 21st Mar 2018, 8:05 pm   #12
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Default Re: Attacking verdigris on complex items?

Good! Thankyou everyone. I think i will go over the silvered fuse carriers with silvo and cotton buds and then try and decontaminate around their mountings with meths and a toothbrush. Don't fancy getting water on bakelite it it can be avoided.
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Old 21st Mar 2018, 8:25 pm   #13
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Default Re: Attacking verdigris on complex items?

Cillit Bang?may work.
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Old 21st Mar 2018, 8:48 pm   #14
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Default Re: Attacking verdigris on complex items?

Hi.

It's good to know that the lemon juice tackled the problem. I've come across this verdigris corrosion on several battery connections over the years which I think can be made worse by leaking alkaline batteries. I believe zinc carbon type batteries may create less corrosion should they leak.

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Old 21st Mar 2018, 9:24 pm   #15
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Default Re: Attacking verdigris on complex items?

I agree. With alkalines you sometimes get the blue stuff , even more destructive than green. Hydroxide no doubt.
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Old 21st Mar 2018, 9:59 pm   #16
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Default Re: Attacking verdigris on complex items?

Quote:
Originally Posted by Philips210 View Post
It's good to know that the lemon juice tackled the problem.
To be exact, the citric acid in the lemon juice tackled the problem.
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Old 21st Mar 2018, 10:01 pm   #17
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Default Re: Attacking verdigris on complex items?

Hi

Something else I've noticed on the plastic battery holders is the appearance of water droplets seen on the plastic. The holder had suffered from green corrosion on some of its terminals from a leaking alkaline cell. Perhaps the residue on the plastic is very hygroscopic and especially noticeable when left in a damp atmosphere. It reminds me of a similar situation if table salt deposits are left in a container in a damp place.

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Old 22nd Mar 2018, 4:18 pm   #18
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Default Re: Attacking verdigris on complex items?

Quote:
Originally Posted by HamishBoxer View Post
Cillit Bang?may work.
Caution. I think it's conductive. (Just in case it can't be removed from crevasses in insulation.)

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Old 22nd Mar 2018, 8:44 pm   #19
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Default Re: Attacking verdigris on complex items?

Courtesy of blu-tack, a mock up of the finished article.

Fuse carriers cleaned up with silvo wadding, with the exception of one on which the (sulphide?) required abrasion with a blade. Final wash with meths now,to get under and around all the bits which i haven't stripped off.

(Yet again the camera has spotted corrosion inside a fuse which i could not see myself)

One of these assemblies had silver plating on the brass rivets, which has protected them quite well. (These are 1968 avometers, but even at this point no two meters were exactly the same)

If there is any deterioration i will report back, but i am fairly confident!

Dave
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Old 26th Mar 2018, 4:12 pm   #20
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Default Re: Attacking verdigris on complex items?

Having worked on some more heavily corroded parts, i have inadvertently managed to copper plate the scraper blade by exposure to the used solution! Now if you wanted to copper plate something this well, you can bet summat would go wrong.

I don't think i will be throwing away the solution just yet, it's too useful..
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