Weird Yellow Discoloration on Copper

Hi, I recently started using some copper sheet (C101 oxygen-free H00 alloy) that reacted in the sodium bisulphate pickle. The reaction revealed itself when I took the sheet out of the pickle and started neutralizing with baking soda. The copper started “shedding” bright yellow pigment - to the point that my hands were bright yellow as well - I had to wash them with soap to remove the yellow stain. When the metal dries it almost looks like it has been treated with liver of sulphur.

In decades of work with copper - all conditions being basically the same - I have never experienced this. I asked the supplier and unfortunately I purchased the material a few years ago and health and safety data are not available any longer for that batch of alloy. I am making an assumption that the copper is the alloy I have described - which, when I research the allow - they describe it as being 99.95 pure.

What is it? Cadmium? Any ideas or similar experience?

I’m also never seen such a thing, and I only work in copper.
My first thought would be it was a different alloy then they told you.
Maybe copper plated tin ??

Have you tired to repeat it with the same pickle & different copper sheet ?
Have you tired to repeat it with new pickle & the same sheet ?

Results would be educational .


1 Like

Did you use a brass brush when you took the copper out of the pickle? I did just that and discovered a beautiful golden sheen on my practice piece. I thought it was quite lovely, but completely unexpected.

| liveoak
April 24 |

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I’m also never seen such a thing, and I only work in copper.
My first thought would be it was a different alloy then they told you.
Maybe copper plated tin ??

Have you tired to repeat it with the same pickle & different copper sheet ?
Have you tired to repeat it with new pickle & the same sheet ?

Results would be educational .


Just an observation… I read your spec number to my husband… He says it’s refrigeration tubing copper. Compare that to what Rio Grande sells for jewelry making… I think they will be different. I also wonder if it’s something youd want to contact the skin. I would be interested in hearing the results of your comparison.

Good luck!

Hi Patty,

Thanks for the feedback

The metal store has confirmed that it is “roofing copper”.
I pickle copper all the time and other copper I have is responding the same way it always has.
Honestly, I am not going to be doing any testing in my studio with this copper - the coloration actually freaks me out somewhat and I don’t want to expose myself to what might be toxic chemicals released by the reaction with the sodium bisulphate.

Hi REDesigns,

The copper came in sheet form and it has been identified as roofing copper.

I’ve been following this thread since the beginning. Like others I do a lot of work in copper. I’ve also done a lot of work in roofing copper. I think you are looking at the wrong part of this puzzle. One of the weirdest things that ever happened to me was pickling my copper and ending up with a bright, and I mean bright in your face Chartreuse green color. It was so invasive, I couldn’t get it off the copper. I tried to torch it off. I tried to repickle with new clean pickle, I tried to file if off. Nothing worked. It wasn’t a pretty color. It was more yellow than green. Now what did I do that you did? We both used a bisulfate pickle. I got the first time from Otto Frei. The second time I went to a local swimming pool supply store. The first time it happened, my daughter admitted she had left the steel tongs i use in soldering in the pickle to try and make them shinny bright. It contaminated the pickle. It was really badly contaminated since she had left those tongs in the pickle for nearly 2 days. I had a migraine, and she did it without telling me. She also at the same time had taken my car and gone joy riding. She was a couple weeks short of 16years old. Ok now for the second time. It was here in Florida. I ran out of pickle which led me to need it quicker than normal. It coincided with me dumping the contents of my rotary tumbler out near my pickle pot, nd a few of the steel shot (I didn’t see it happen) fell into the pickle pot which pointing a finger at myself, forgot to replace the lid on the pickle before i did the tumbler dump. Now another variable that happened, was both pickle pots had after introduction of the steel been turned off. The green happened when I turned the pickle pots on that were contaminated. Next variable was the bisulfate. Mine component of the bisulfate is sulfur. Sulfur is yellow. Your yellow might be coming from that sulfur. Just like with mine it was the green from the copper, and the yellow from sulfur I got the cross of the two colors. I’ve tried few times to create the same effect. I get varying results. It’s kind of a serendipity happening. The sulfur that ends up in yellow on your copper is sulfur salts. I wouldn’t fear it, but I wouldn’t make it into something I was going to sell. It could create a dermatitis condition on your skin. This is all my thoughts, and use it for what it is.


“Roofing Copper” is really just the reference to it being a specific thickness (22 mil). Unless it’s mis-marked, it’s still basic 99.9%+/- pure copper.

Ron Charlotte

Gainesville, FL OR

Now that’s interesting Aggie. I love that you figured out why, and shared your results - it helps us all learn .

I might have to try contaminating a pickle pot and see if I like the patina :slight_smile:

Thank you for posting your findings,

Hi Aggie,

I have been using the same sodium bisulphate as a pickle for about 15 years. I also work with various chemicals to create patinas for bronze and copper. I am not a chemist or metallurgist, so I thought perhaps I might be able to access the “mindmeld” on the Orchid forum. Thanks for your observations!

My own experience and knowledge as regards steel in the pickle is that it causes an electrolytic reaction when it is in the pickle which causes copper oxides suspended in the solution to plate to the objects that are in the pickle while the steel is in the pickle - not that if a piece of steel is placed in the copper it contaminates the pickle “forever” until you change it. Best practice in my own studio is not to use steel tweezers or steel binding wire etc in the pickle at all.

So I don’t think that the pickle itself is the problem - also because other copper in the studio, placed in the pickle at the same time did not exhibit the characteristics that I describe in my original post. So, I am still thinking that it is the copper that is the issue.

From wikipedia:
" Sodium bisulfate, also known as sodium hydrogen sulfate, is the sodium salt of the bisulfate anion, with the molecular formula NaHSO₄. Sodium bisulfate is an acid salt formed by partial neutralization of sulfuric acid by an equivalent of sodium base, typically in the form of either sodium hydroxide or sodium chloride. Wikipedia"


Hi Ron,

Yes, which makes the reaction even more mysterious. There is no guarantee it was roofing copper, however.


A few thoughts on it. use super copper saturated pickle. The really blue pickle. also I turned off my pickle pot and the steel was still in both times. It sat for a few days. When i turned it back on, that’s when the patina occur. It is a disgusting color. more yellow than green. Excuse my dairy reference I grew p on one until i was 10. It is what we call cow sh*t green, well aged.


Hi Donna,

It wasn’t me that used the steel tweezers. It was my teenage daughter. That’s why I always say, A hammer, an anvil and a blow torch, are better than Prozac when you have teenagers. That’s how she made it to adulthood, Momma smashed metal.


well you don’t make it sound worth trying - cow sht green doesn’t sound so beautiful & I also lived on a diary farm for some years !

Maybe if I’m bored one day - I do save some of my super saturated blue pickle in a jar - so I have it to start with.

Thanks for the tip - I think :face_with_diagonal_mouth:


It all has to do with the electromotive reaction series for ions and metals.
In a solution of mixed precious metal ions and other ions, if you insert a piece of Copper all the precious metals + Mercury will drop out by plating on the actual copper.
Swap electrons with the Copper so one metal goes into solution and the other comes out.
Unless the surface are carefully prepared (Flash plating) and/or plated with Nickel
or other barrier metals it will usually not stay there much, just end up as fine mud in the bottom.

On the other hand Iron/Steel will drop even more metals (among them Copper) since it is closer to
Hydrogen in the electromotive series.

I have never heard about dropping to secondary metals (to Copper from Iron)
but it seems plausible if the metals are in physical contact.

The yellow may or may not be Gold, Silver or Tin (flash plated) if the pickle
somehow picked them up in the past, a thin layer of Silver or Tin may color the Copper
yellowish maybe. Just thinking out loud here.

Regards Per-Ove

Now that is really really weird! NaHS04 is just usual pickle, used for silver, gold and virtually all “normal” precious metals. H2S04 is sulfuric acid and will work just as well but is too acidic to be safe. (before saniflush was reformulated, it was NaHS04 and far cheaper than buying pickle from a supply store… it worked just as well)…It can’t be sulfur in native form. the redox potential for S04 to S is -2.2V which pretty high, Fe going to Fe+2 has a redox potential of +.4V. Fe+2 is soluble and has a yellowish tint. Fe 3+ is rust Fe203 and is insoluble… even with iron metal contamination, it’s not possible to reduce sulfate to sulfur. (In nature, the sulfate in gypsum, CaS04.H20, is reduced to native sulfur by anaerobic bacteria feeding on hydrocarbons in salt domes, which is why salt domes are drilled looking for oil deposits) Fe+3 to Fe+2 is -0.7V… the redox potential of Cu (metal) going to Cu+1 (blue color) is -0.37V and for Cu+1 to +2, 0.15V…so far as the yellow stuff being sulfur salts, sulfur salts are sulfides… like pyrite, chalcopyrite…gold, copper and silver, have low redox potentials and will dissociate into metal and native sulfur under reducing conditions, with the exception of silver which will bind to sulfur strongly making black tarnish…(tarnished silver can be easily cleaned by putting it in an aluminum pie pan with baking soda and warming it… the sulfur transfers to the aluminum, which is highly reactive in a mild alkaline condition.) It might be worthwhile to see if you get the same results with clean fresh pickle… if it happens again, then you could test it… dry the yellow stuff off and see if it burns… sulfur dioxide is acrid… you would be able to smell it. Put some on a charcoal block and heat it with a reducing flame to see if it turns into a metal…flame tests can also tell you what metal species are present, but the Na from the pickle has to be washed out with distilled water on a piece of filter paper, otherwise the yellow color of Na will overwhelm any other metals present… copper will be greenish blue. Gold and silver are non reactive… cadmium is brick red in a flame…not likely to be Cd, since that amount of it is LOT and would make an alloy toxic… or send it to your local university chemistry department and ask them what they think it is…