Help Brass sometimes turns dark copper color in ultrasonic...Why?

[BCR]

I have been repairing clocks for 32 years. On occasion, I will place a dirty clock movement in my heated ultrasonic cleaning tank and after 3 to 4 cycles (for a really dirty movement) the brass will start to turn a dark copper color, and sometimes nearly black. I use non ammoniated water based cleaner because the strong smelling ammoniated cleaners are just too much for indoor use. I am currently using POLY-CHEM DEOX-007. And this discoloration just happened in an almost brand new batch. Anyway, when this happens, I spend a lot of time with a toothbrush and various cleaners to remove the discoloration. Actually, when this happened to me just a few days ago, I did mix a small batch of ammonia based cleaner outdoors in a plastic bucket, soaked the badly discolored movement in that for about half an hour and it was back to gleaming brass. Does anybody have any ideas what it is that causes this discoloration to happen? I do think a common theme for me when this has happened, is that someone in the past has done some soldering on the old brass movement. Could it be that the lead based solder has a reaction with the cleaning solution? Any ideas would be appreciated.
Also, if anybody knows where I can find HISTORIC TIMEKEEPERS ultrasonic cleaning solution it was always my favorite, but seems to be out of production

 

[Kevin W.]

Chemical reaction between brass and steel?

 

[novicetimekeeper]

Copper II Oxide is black. Copper showing in brass suggests dezincification.

 

[shutterbug]

There are also plates that are not brass, but have a brass look to them because of a coating the factory applied. When that thin coating is compromised, you have the original metal exposed.

 

[R. Croswell]

On occasion, I will place a dirty clock movement in my heated ultrasonic cleaning tank and after 3 to 4 cycles (for a really dirty movement) the brass will start to turn a dark copper color, and sometimes nearly black.

I hope you are not placing the complete assembled movement in the ultrasonic. I've seen this copper color discoloration only a few times. Each time there was a zinc, magnesium, aluminum, or other non-ferrous reactive metal present. I believe it is an electro-chemical reaction between the different metals. The pH of the cleaning solution is likely a factor. Brass and steel do not seem to be a problem together, only alkaline metals like zinc, magnesium, and aluminum. Solder (lead and tin) is pretty unreactive. I have not had a problem as long as I only put brass and steel in the cleaner at the same time.

RC

 

[RickNB]

Ran into the same problem today. 3 batches of parts went in to the ultrasonic. The first was fine. The second came out with everything looking like it was copper. Third batch was fine. Same batch of cleaning solution in all cases.

I am concerned about the copper caoting. I can polish it off with a fine abrasive. Is there something else I can do to remove the copper? Is it something to be concerned about - can I just leave it? I assume that copper coating is in the bushings as well.

 

[R. Croswell]

Ran into the same problem today. 3 batches of parts went in to the ultrasonic. The first was fine. The second came out with everything looking like it was copper. Third batch was fine. Same batch of cleaning solution in all cases.

I am concerned about the copper caoting. I can polish it off with a fine abrasive. Is there something else I can do to remove the copper? Is it something to be concerned about - can I just leave it? I assume that copper coating is in the bushings as well.

Please read post #1 "Actually, when this happened to me just a few days ago, I did mix a small batch of ammonia based cleaner outdoors in a plastic bucket, soaked the badly discolored movement in that for about half an hour and it was back to gleaming brass".

I do not believe that the cleaning solution is the problem, only one of three batches experienced the problem. Please read post #5, then let us know just what metals, other than steel and brass, were in that second batch, what cleaning solution you are using, and how hot the solution was.

RC

 

[Willie X]

Try a 6 minute run time at room temperature. Go another 6 minutes if necessary.

IMO, a lot of people are using way way to much heat and run time.

It's not that you are making copper, you are loosing zinc.

Willie X

 

[Schatznut]

Willie has nailed it - the zinc is being leached out of the brass. There's too much of something in your process - chemicals, heat, ultrasonic abrasion... or some combination thereof. Moderation, moderation, moderation. (No, not you, Pee-tah!)

 

[R. Croswell]

Try a 6 minute run time at room temperature. Go another 6 minutes if necessary.

IMO, a lot of people are using way way to much heat and run time.

It's not that you are making copper, you are loosing zinc.

Willie X

Too much time and too much heat surely exacerbate the problem, but I do not believe that is the primary cause of the problem or we would see it happen whenever too much time and too much heat are used.

The copper color is surely copper, but is it brass that has had the zinc displaced, or is it brass that has become copper plated? If the zinc was displaced, where did it go? If it is copper plate, where did the copper come from?

This is perhaps the worst case I have seen. It is a Sessions 2-train chime clock that I own, but this happened before IO got it, so I don't know what solution it was in, but it was clearly a dunk-n-swish without disassembly Note that the copper plating is most intense in the area of the "bright metal" chime drum. Not sure if it is aluminum, magnesium, zinc, or some combination alloy. Even the brass drive arm got copper plated. Also, the "bright metal" chime drum was very clean, perhaps slightly etched. I am positive that the metal chime drum was involved in some way with a chemical reaction that caused all this copper plating discoloration of the brass. The second picture shows the same copper coloring on the steel arbors that extended through the plate near the chime drum. There surely was no zinc or copper in the steel.

I can't explain what happened, but the only source of copper is the brass parts of the movement. Copper ions had to be displaced from the brass and attracted to parts near chime drum which somehow became oppositely charged due to an electro-chemical reaction with the "bright metal" chime drum and the cleaning solution (the electrolyte), and the other brass of the movement.

More questions than answers I'm afraid.

RC

 

[Raymond101]

Hi I don't use one of these cleaners.
But I think you may have a GROUND FAULT on your machine . Ultra sonics work @ high frequencies and dissimilar metals as mentioned above will become NEGATIVE charged allowing molecules to move freely.
Make sure the BASKET & CASE are GROUNDED otherwise electrolysis will have a field day .
Note mains Neutral is not pure ground
Even though in some countries it goes to the Neutral buzz bar there is a potential due to ground leakage protection system.

 

[R. Croswell]

Hi I don't use one of these cleaners.
But I think you may have a GROUND FAULT on your machine . Ultra sonics work @ high frequencies and dissimilar metals as mentioned above will become NEGATIVE charged allowing molecules to move freely.
Make sure the BASKET & CASE are GROUNDED otherwise electrolysis will have a field day .
Note mains Neutral is not pure ground
Even though in some countries it goes to the Neutral buzz bar there is a potential due to ground leakage protection system.

That's an interesting thought and stranger things have happened, but I do not believe that is what's going on here for several reasons.

1) Although there can be some internal electrical leakage from the 120v mains elevating the US tank to an electrical potential higher than earth ground, a ground fault cannot exist without a pathway to earth ground. The tank (grounded or otherwise) and all of the parts in the tank, and the solution in the tank, being in contact with the tank are at the same electrical potential as the tank so there is not fault current path to earth ground. Now if the parts were in a metal basket, and the basket was not in contact with the US tank (insulated from the tank) and the basket was connected separately to an earth ground, yes, the parts in contact with the basket could be at an electrical potential different than the US tank and there would be a ground fault. That's a lot of ifs that are not likely to exist accidentally. Of course for personal electrical shock protection the US should be properly grounded.

2) I'm afraid the chemistry is a bit more complicated and involves dissimilar metals and an electrolyte, very much like a battery. Under the effect of an electrical current the metals can form ions, which are atoms of the given metal that either have more electrons (negative charge), or fewer electrons (positive charge), than their natural molecules. The positive charged particles become attracted to the negative charged particles where they hope to pickup (or lose) an electron to become a neutral atom/molecule again. Negatively charged particles are not attracted to one another. For the electrolysis (electroplating) to work there must be a conductive electrolyte capable of exchanging the ions from one metal to another. A solution with a pH higher or lower than "7" can potentially be such a solution. Which is why this phenomenon would not occur in a petrol based cleaner (which should not be used in an ultrasonic for fire safety reasons).

3) Whatever is going on in the US tank is effectively shielded by the metal tank from the outside world and has to be taking place between the parts and chemicals in the tank.

4) While the pictures in post #10 show the "plating" before the clock came to me, I have seen this same thing happen a few times in my US. The common denominator was that there was always an alkaline metal (Aluminum, zinc, magnesium, etc.) part among the brass and steel parts in the tank. I've always used Historic Timekeepers or Deox-007 cleaning solutions. And my US is grounded.

My advice to avoid this problem is, do not place alkaline metals in the cleaner along with brass, avoid heating the cleaning solution above room temperature, avoid prolonged run times in the US, and make sure the US is properly grounded for personal safety. The last three probably have nothing to do with the copper plating problem but will help protect the brass from getting that "cooked" appearance from over cleaning, and help ensure personal safety.

That's what I think

RC

 

[Raymond101]

The ultra sonics cleaners consists of 2 ceramic transducers that run at a frequency of 60khz to 200khz .
200khz is the more professional unit .
The whole thing relies on cavertation ie the higher frequency makes smaller bubbles. Keeping it simple. The non professional US have pore PWM and if the power supply is faulty ie the caps and other electronics the transducers can become loose and also the can run @ cross frequencies. If you read up on the exact problem that can accure the bubbles can boil on the surface due to eather ground fault that is generated with the power supply. As you can not hear or see . Some cavitation on the brass can reach much higher that you think . If the unit is more than 4 or 5 years old it should be checked. If the transducers are damaged or have a 2nd harmonic this is 400khz and this will pull the zinc and softer metal out much quicker.
The electro plating can be caused by due to the smaller cavitation .
Not knowing which US your using but the control system in US are the same principle.
Except the big pro units are better built and are far more stable.
If there is a problem the time should be reduced to compensate. Or get someone to check the working fq is with the rating of the US unit in question..

 

[Schatznut]

The alkali metals are in group Ia of the periodic table - Li, Na, K, Rb, Cs and Fr. Na and K are commonly associated with Cl, and are used as pH buffers in many solutions. This suggests that we understand the pH of our solutions as a data point to help understand the discoloration we sometimes see.

Leaching of zinc is a common problem with brass, and in "free-machining brass," there is a small amount of added lead (Pb) that serves primarily as a lubricant. Lead leaches out of brass when in contact with water, especially ultra-pure water, which can lead to stress corrosion cracking.

 

[R. Croswell]

The alkali metals are in group Ia of the periodic table - Li, Na, K, Rb, Cs and Fr. Na and K are commonly associated with Cl, and are used as pH buffers in many solutions. This suggests that we understand the pH of our solutions as a data point to help understand the discoloration we sometimes see.

Leaching of zinc is a common problem with brass, and in "free-machining brass," there is a small amount of added lead (Pb) that serves primarily as a lubricant. Lead leaches out of brass when in contact with water, especially ultra-pure water, which can lead to stress corrosion cracking.

One thing for sure, zinc and or lead did not leach out of that steel arbor that got copper plated.

RC

 

[R. Croswell]

The ultra sonics cleaners consists of 2 ceramic transducers that run at a frequency of 60khz to 200khz .
200khz is the more professional unit .
The whole thing relies on cavertation ie the higher frequency makes smaller bubbles. Keeping it simple. The non professional US have pore PWM and if the power supply is faulty ie the caps and other electronics the transducers can become loose and also the can run @ cross frequencies. If you read up on the exact problem that can accure the bubbles can boil on the surface due to eather ground fault that is generated with the power supply. As you can not hear or see . Some cavitation on the brass can reach much higher that you think . If the unit is more than 4 or 5 years old it should be checked. If the transducers are damaged or have a 2nd harmonic this is 400khz and this will pull the zinc and softer metal out much quicker.
The electro plating can be caused by due to the smaller cavitation .
Not knowing which US your using but the control system in US are the same principle.
Except the big pro units are better built and are far more stable.
If there is a problem the time should be reduced to compensate. Or get someone to check the working fq is with the rating of the US unit in question..

We can agree to disagree, but I do not believe that a defect in the ultrasonic cleaner caused this problem.

RC

 

[demoman3955]

given that Brass is composed of copper and zinc, id think one is leaching out of the other. I use ammonia to clean a lot of stuff, and found that too long in ammonia will turn some things that are non ferrous and composed of more then one element to turn black.

 

[R. Croswell]

given that Brass is composed of copper and zinc, id think one is leaching out of the other. I use ammonia to clean a lot of stuff, and found that too long in ammonia will turn some things that are non ferrous and composed of more then one element to turn black.

“Leaching” is more of a dissolving process separating one substance from another. Ammonia is a highly reactive chemical compound. When there is a color change, I rather suspect that the Ammonia is chemically reacting with the material to form a new compound that is black. The end result is the original material is eroded, changed, or otherwise damaged.

RC

 

[Schatznut]

One thing for sure, zinc and or lead did not leach out of that steel arbor that got copper plated.

RC

Roger that!

 

[RickNB]

Further to my recent experience...

I took a look at the 3 batches I put in the ultrasonic. The first and third batches were only brass and steel pieces, and they cleaned fine. But the middle batch, the one that got copper-covered, had steel and brass that had small traces of solder on it, and the gong hammer (lead?). Perhaps the hammer caused a reaction. I think I'll try dropping some scrap brass and a piece of lead in the ultrasonic and see what happens.

 

[Raymond101]

Question what water do you use ie tap water city . Filtered water to dilute the cleaner. Etc.
Also what type of US are you using.
What frequency is it operating at?
What temperature is the solution?
Just dump random test may not solve .
There maybe something like every thing that you haven't told the smallest might be the problem.
On one of your photos I zoomed on the copper plating it had rotation rings which is odd in its self . Which would only because of spinning cavertation.
No sure how you could have this effect.
How big is your US tank ? And are the cleaning items going into baskets or something else.
Just interested. What you are actually doing.
I have worked on industrial equipment only . In intel awhile back . But never seen rotational plating. It is possible that the brass bushing below was spinning on the shaft during cleaning.
.
Lead solder is 60 /40 ie lead / tin
The hammer sticker probably not pure lead but a mix
Tin is also used in older brass as well as zinc . If very old before quality control will be many other impurities.
Also was the brass plated? With gold .etc.
.

 

[R. Croswell]

Further to my recent experience...

I took a look at the 3 batches I put in the ultrasonic. The first and third batches were only brass and steel pieces, and they cleaned fine. But the middle batch, the one that got copper-covered, had steel and brass that had small traces of solder on it, and the gong hammer (lead?). Perhaps the hammer caused a reaction. I think I'll try dropping some scrap brass and a piece of lead in the ultrasonic and see what happens.

I'm pretty sure the gong hammer is the problem, probably made of zinc. I've had this happen a couple times when I cleaned a batch with a zinc gong hammer. In your test, it may not be just the presence of the gong hammer, but what other pieces were electrically in contact with the hammer head or the steel hammer shaft.

RC

 

[R. Croswell]

Question what water do you use ie tap water city . Filtered water to dilute the cleaner. Etc.
Also what type of US are you using.
What frequency is it operating at?
What temperature is the solution?
Just dump random test may not solve .
There maybe something like every thing that you haven't told the smallest might be the problem.
On one of your photos I zoomed on the copper plating it had rotation rings which is odd in its self . Which would only because of spinning cavertation.
No sure how you could have this effect.
How big is your US tank ? And are the cleaning items going into baskets or something else.
Just interested. What you are actually doing.
I have worked on industrial equipment only . In intel awhile back . But never seen rotational plating. It is possible that the brass bushing below was spinning on the shaft during cleaning.
.
Lead solder is 60 /40 ie lead / tin
The hammer sticker probably not pure lead but a mix
Tin is also used in older brass as well as zinc . If very old before quality control will be many other impurities.
Also was the brass plated? With gold .etc.
.

First, BCR hasn't posted any pictures yet, perhaps he will, so you are discussing the picture I posted in post #10. The 2nd. picture below shows where the shaft with the "rotational plating" lives. The clock was very dirty when I got it, and the lifting lever shown at the arrow was probably in contact with that shaft. I suspect one of two possibilities explains the rotational plating; 1. a combination of streaked oil and dirt prevented uneven plating, or 2. rotational markings happened after the part was plated (I'm assuming that the clock actually ran for some period of time before it became this filthy and was sold).

If any of the many variables that you mention are causing BCR's "plating problem", one would expect similar results in all three batches, not just one batch. The only variable isolated that was different in the batch that "plated" was the presence of the (probably zinc or zinc alloy) hammer head. The only explanation that seems to account for what BCR is reporting, including the copper plating of steel and brass parts in my example, is an electrochemical reaction within the US tank between the metal part that is not brass or steel, and the parts that got plated, and the solution (electrolyte) that filled the tank. The composition of the hammer head (and in my case the chime drum), the composition of the cleaning solution, and the physical arrangement of the parts in the basket are unknowns that make discovering the chemical equation difficult.

RC