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topic 15330

How can I make sheet copper turn matte black?

A discussion started in 1998 but continuing through 2017


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


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 Hao
- Grand Rapids, Michigan


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

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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?


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


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

Jax Green Patina


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


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

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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 [linked by editor to product info at Amazon]] would be sufficient enough for this purpose.

Thank you

Jairo Velasco Jr.
research assistant - Syracuse, New York


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, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


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

Blackening copper for computer cooling


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


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

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


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 protective gloves [linked by editor to product info at Amazon] and safety goggles [linked by editor to product info at Amazon]! Work outside or under strong ventilation.
immersion silvering for copper:
15 gm silver nitrate
30 gm sodium thiosulphate
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


A. For those who are looking to turn copper black go to an art supply store and ask for Liver of Sulphur [linked by editor to product info at 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

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

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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