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topic 15330

How can I make copper turn matte black?

Current question and answers:

January 31, 2021

Q. Hi,

I am interested in a finish I have seen others achieve on carbon golf putter heads by using black oxide. How are they able to achieve a dark black shiny/glossy finish? Many thanks

David James
- London, UK

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January 2021

A. Hi David. I don't know exactly what golf club manufacturers do, but the hot black oxide process can be done directly on steel, and centers upon putting the object into boiling caustic soda plus nitrogen-based oxidizing agents to generate black rust on the surface. If the object was very highly polished before hand, it comes out a jewel-like blue black; if matte finished before immersion it comes out matte black. This finish is common on firearms. It is possible additionally to lacquer it or apply higher technology clear coats for other purposes.

But there are many other routes to a black metallic finish: copper plating followed by blackening, zinc or zinc-alloy plating followed by black chromate conversion coating, black nickel plating, black chrome plating, etc.

Please help us help you by telling us why or in what way you are interested -- as a hobbyist who wants to try it, a plating shop who wants to find a process supplier so you can offer this process, a manufacturer looking to find a shop to do this finish for you, etc. Thanks!

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey




Previous closely related Q&A's starting in:

1998

Q. I have a copper panel that is kept at liquid nitrogen temperature when used in a vacuum system. One of it's purposes is for heat removal. There are indications that copper is a very good reflector of infrared radiation and thus a poor absorber. I am looking to increase the absorbtion of IR possibly by blackening the copper. I have heard that this can be done electrolytically. Is this true? Can it also be done by wiping liquid over the surface much like blueing steel (i.e., does it come in a bottle or do I have to send out the whole panel?)?

I also have some concerns about whether the 'blackened copper' will cause great problems in a production vacuum system like outgassing, flaking, etc.

Any other comments are always appreciated.

John Davis
John Davis
- Berthoud, Colorado, USA

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1998

A. John,

Try an immersion blackening liquid with copper panels: 1.6 - 1.9 g/L liver of sulfur or liquid polysulfide solution at around 25 °C for 50 to 80 seconds. As long as you optimized the conditions to get the color you want, you can blacken your parts.

Good luck!

Ling

Ling Hao
- Grand Rapids, Michigan


1998

A. Dear John,

The solution offered by Ling is correct for blackening copper, however I suspect that because it is a simple conversion coating there might be problems with the adhesion, if you are looking for a coating that is black and adherent, then I would be looking towards Black Chrome Plating, provided the panels are not subjected to a lot of flexing and that the temperature can be GRADUALLY decreased then it may work.

best regards

John Tenison-Woods
John Tenison - Woods
- Victoria Australia



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



Blackening of copper

2000

Q. I have been asked to look into ways of blackening fine copper mesh. Any suggestions would be gratefully received. Thanks.

Nick Cooper
- Bridgend, Wales, UK
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2000

A. Investigate the black oxide formulations offered for multilayer printed circuit board manufacturing. They are reasonably easy to control and adherent.

The real question, and not easily read from your post, is why you want a blackened copper mesh. One of the problems with answering questions here is what do you really want? The more information you give us, the better the information you get. Right, Ted?

James Totter
James Totter, CEF
- Tallahassee, Florida


2000

A. Hi, James. Yes, it's most efficient to give as much detail as possible :-)

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2000

Q. Thank you I do appreciate it that the more information the better. However, the customer who would like this done is unwilling to divulge more for confidentiality reasons. I too would like to know why he want's it! Thanks again

Nick Cooper [returning]
- Bridgend, Wales, UK
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2000

A. Unfortunately it can be dangerous if they won't tell you the application, Nick. But in addition to Mr. Totter's suggestion, you've got painting and powder coating; a half-dozen different ways to patinize, either through chemical or flame blackening; zinc plating with black chromate; cad plating with black chromate; black nickel plating; black chrome plating; lamp black; black rhodium or ruthenium, PVD coatings, and our favorite finish, dipping in chocolate :-) smiley.

If there is a need for confidentiality, one approach is to retain a metal finishing consultant and have him/her execute a non-disclosure agreement, and be able to work from all the facts :-)

Good luck!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


sidebar 2000

thumbs up sign Ted,

What is the corrosion resistance of the chocolate dip for 10% white salt? Is there a difference if you use milk chocolate or dark? I really need to know. (It will be a wonderful way to get rid of some of the "unneeded" candy after next Halloween!

Gene Packman
process supplier - Great Neck, New York

2000

A. Hi Gene!

There are several idiosyncrasies with chocolate post dip. First, salt spray is not a good test since the chocolate will melt and wash away. That's bad. This leaves only the colder areas of the country where it might find any use at all. Then, chocolate is poisonous to dogs, so it can only be applied to areas which cannot be reached by Fido, or Rex, Spot, Tickles, etc. That's bad. In use around the exposed undercarriage of logging trucks, it is a ready and high calorie source of food for the spotted owl. That's good or bad, depending on how you voted in the last presidential election :-0

tom pullizzi animated   tomPullizziSignature
Tom Pullizzi
Falls Township, Pennsylvania


May 2, 2010

thumbsdown My lord. "How to blacken copper". Who cares why? Just answer the guy's question!

don paterson
- Elmira, New York


April 2, 2010

Hi, Don.

Should I travel by ship or by train? I don't yet know whether I'm going from Miami to Cuba, or from Miami to Memphis, but just answer the question :-)

Although we gave Nick a dozen ways to blacken copper, we care because:
- If he uses the cadmium plating that we mentioned, or the patinizing process involving arsenic or tellurium that we suggested, and this mesh is used to filter a food product, he'll poison people and they may die.
- If he picks a coating we know to be fairly temporary, and Nick warrants it for 10 years, we've served him poorly.
- If this screening is to be placed behind a viewing glass, or used in a solar collector, and he picks one of our suggestions with a high vapor pressure (like paint or powder coating) it may quickly coat and obscure the glass, rendering the whole effort worthless.
-If he uses it in a vacuum environment, the cadmium and zinc coatings that we suggested will sublimate, which could cause a disaster.
- We also suggested several coatings that are only good for 140 °F -- what if his customer intends to use the mesh at a higher temperature than that?

Please understand that there is no "right" finish or "better" finish; every finish offers advantages & disadvantages that are crucial in some applications but of little or no importance in other situations :-)

Thanks and regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


January 11, 2012

Q. Hi, I have the same question. I have no problem disclosing the needs of the finish though. To suit my need the less reflective, with high light absorption the better. I would like to it be UV stable and last for as long as possible, 20 years or better. It would be exposed to around 150° F and possibly 200 or higher. I don't want poison gases or particles floating around the most of all! Thanks!

Michael Davidson
- Dayton, Ohio, US

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March 7, 2012

A. Hi, Michael.

Black chrome plating sounds quite right to me. It can be very matte & very black, and is used to line the inside of microscope and telescope tubes. The temperature is no problem. You might wish to listen to our podcast on black chrome.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2002

Q. When I was in middle school we had an art class where we took a sheet of copper (I think) and wiped it with some liquid that made it turn matte black instantly. We then scraped off the black coating with a sharp tool, thereby re-exposing the copper beneath. Does anyone know how to chemically turn sheet copper black?

Thanks.

Jim V [last name deleted for privacy by Editor]
- Boston, Massachusetts USA

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2002

A. Quickest way to blacken copper is using a sulphur solution. You didn't say how big a piece you wish to blacken. If only a small solution is needed, you may be able to make a solution using match heads and hot water to make a weak solution. You will probably have a hard time finding sulphur or polysulfides to make a true solution. It will work better if the copper is clean prior to wiping with solution. If you don't care about surface texture, the best thing is to sand or preferably sand blast prior to blackening. The duller the sanding the flatter the finish. Leave solution on copper for a couple minutes, you may need to repeat. Rinse and dry between applications.

Good Luck.

Wayne M [last name deleted for privacy by Editor]
- Mississauga, Ont., Canada



Blackening process for large copper art piece

affil. link
Jax Green Patina

2003

Q. I want to "blacken" a large copper art fountain made of new, cleaned copper. Once I get a black or charcoal base for the copper, I want to highlight with a green patina, giving the piece an ancient look. I've tried Jax Black and Jax Flemish Black, applying several coats. However, the best I can come up with is a rust-color, i.e., darker brown. Is there a product or process I can use that would cover the copper in a black tone, over which I can apply green patina highlights?

Would spray-painting the copper with a matte black work, over which the green could be applied? Then wax the entire surface?

Thanks for your help!

Jurgen Ahlers
- Atlanta, Georgia

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2003

A. You can try with 2% solution of potassium polysulfide. Solution must be applied on torch heated object with brass scratch brush. Matte black color develops quickly, after that surface can be variegated by lightly dabbing with soft cloth dampened with solution.

Goran Budija
- Zagreb, Croatia



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2004

Q. Hi,

I have the task of optically blackening (anodizing?) the inside of a copper can. I was wondering if the use of Liver of Sulphur [affil. link to info/product on Amazon]] would be sufficient enough for this purpose.

Thank you

Jairo Velasco Jr.
research assistant - Syracuse, New York

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2004

A. Hi Jairo. Anodizing involves application of anodic current on the item while immersed in an appropriate salt, so I doubt that that is what you are doing -- and I would not electrolyze liver of sulphur. If the question is whether liver of sulphur will cause blackening of copper, the answer is yes it will, and it's often used for specifically that purpose, but there are both better proprietary blackeners for copper (Ebonol C is an example) and better methods like black chrome electroplating or vacuum deposition of black coatings (Acktar for example). Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



2004

Q. I have a copper table that when we purchased it which had a smeared black finish to it. My cleaning lady to a metal cleaning product to it and it cleaned off the finish and now it's just clear copper. What can I put on the top to re-create the black smeared look? It appears the manufacturer just put some liquid on it and smeared it.

Debbie S [last name deleted for privacy by Editor]
home owner - Menlo Park, California, USA

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Blackening copper for computer cooling

2006

Q. I am interesting in blackening copper parts for a computer cooling system. I do not a protective finish, simply an aesthetic one. I realize that aluminum is much easier to anodize to a black color but copper allows for better transfer of heat. I would prefer a flat/matte finish to a glossy coat. Any ideas? Also, any ideas how to give copper a more silver finish without plating it?

E. Asher Balkin
Copper parts for sub-zero computer cooling research - Columbus, Ohio, USA
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2006

A. There are countless patinas for copper, Asher. Please see if our FAQ on the subject is any help to you.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2006

A. You can use next solution:
25 gm potassium polysulfide
1 lit water
immerse copper in hot solution(oxide and grease free!)
Matte dip for copper:
1 lit sulphuric acid
1 lit nitric acid
2o ml hydrochloric acid
50 gm zinc sulphate
5 gm soot
Add sulphuric acid to nitric (very slowly), when cold add hydrochloric acid, zinc sulphate and soot. Use rubber Rubber Gloves [affil. link to info/product on Amazon] and safety goggles [affil. link to info/product on Amazon]! Work outside or under strong ventilation.
immersion silvering for copper:
15 gm silver nitrate
30 gm sodium thiosulphate [affil. link to info/product on Amazon]
10 gm ammonium chloride
1 lit water
Dissolve nitrate in 50 ml water,add ammonium chloride dissolved in same amount of water,add obtained silver chloride to thiosulphate solution in 0.9 lit water.
Cold immersion!
Good luck!

Goran Budija
- Zagreb, Croatia


2007

A. For those who are looking to turn copper black go to an art supply store and ask for Liver of Sulphur [affil. link to info/product on Amazon]. It will blacken copper almost instantaneously. Test on a corner or a scrap first to give you an idea as to how fast it will take effect. Also make sure your copper is not coated with a lacquer and make sure to use in a well ventilated area (the fumes are not toxic but, being sulphur, the smell is very unpleasant).

Jon Harty
Artist - Coeur d' Alene, Idaho, USA



November 25, 2010

Q. I've read an earlier thread on this subject but couldn't determine the best action. I use 1/4" copper plate for electrical connections which get warm at high current. They are not for use in food processing or medical devices, rather for general industrial size rotating machinery operating in temperatures of -60 °C to +130 °C . I would like to raise the emissivity of the copper plate to improve heat dissipation at the higher temperatures without affecting circuit resistance. I was thinking of coating the reverse side only of the copper plate so that the electrical connections are not affected but I cannot find a cost effective way of achieving this. The coating should be generally durable but not necessarily impervious to minor scratches. Any ideas please?

Stephen Hartley
product designer - Sheffield, South Yorkshire, UK
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Cold blackening of copper is coming out red

January 9, 2017

Q. Hi I am a chemical engineer working in electroplating freshly. I have problem in oxidizing copper with cold method (selenium). Workpiece becomes red, not black.
Please help me to make black oxidation of copper with selenium, copper sulfate, sulfuric acid; and how to make analysis of selenium.

Asmaa el-sayed
- Alexandria, egypt
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April 18, 2017

A. You might try preparing a fresh make up and checking redox potential (ORP) vs. your production tank contents.

Selenite can be tested for via redox titration with permanganate. There is also methyl orange acidity to be checked.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

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