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Finish for a copper radiator/heatsink. Cleaning copper & solder


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October 5, 2021

Q. I'm trying to polish a large intricate copper radiator/heatsink (dimensions 40cm x 40cm x 45cm, please see photo) I made originally 11 years ago (as a project as a fanless watercooled computer case), to polish to a mirror shine before spraying with incralac copper lacquer to prevent oxidation.

The question I have is how best to clean it prior to lacquering. I am manually sanding the copper heatsink (5m^2 surface area) with increasingly fine sandpaper, polish using either brasso or jeweller's rouge or similar, and then ultrasonically clean it. The large heatsink/radiator was made by soldering copper heatplates to copper tubing using 95% tin, ~3% silver and ~2% copper solder, using a rosin-based flux paste and a propane/butane blowtorch to melt the solder. This had left thick brown crystalline solder residue, I suspect from overheating during manufacture. This has largely been removed mechanically from sanding, but the heatsink is difficult to get to sand parts of effectively due to the intricacies if the heatsink/grid shape.

55866-3b   55866-3f   55866-3a   55866-3c   55866-3e   55866-3d

I have experimented using various cleaning solutions and acidic/alkali cleaning solutions and rinsing off afterwards using a steam cleaner/ hot water pressure washer. I have found oxalic acid based cleaners (barkeepers friend liquid paste) effective at cleaning but leaves the 95% tin solder joints blackened and although deoxidized the copper loses the mirror shine from polishing/buffing and become pink rather than the mirrored pink of buffed copper. I want a mirror shine really.

1) Should I assume blackening of tin solder joints and loss of mirror shine will be the case also if using an acidic/oxalic acid based cleaning solution if cleaning ultrasonically?

2) Will ultrasonic cleaning with a pH neutral cleaning solution thoroughly remove polishing compound residue, or should I look to thoroughly removed polishing compound with eg cellulose thinner/acetone/isopropyl alcohol beforehand? (I hope to polish, ultrasonically clean and then lacquer ASAP afterwards)

Many thanks,

Dr Tom Gravgaard
- Bournemouth, England

Closely related Q&A's, oldest first:


Q. My friend and I are in the process of completing sculptured designs for central heating radiators made from copper tubing ... but we have a problem. The overspill of the silver solder we use to fix the copper cap ends to the pipes needs to be removed prior to chrome plating. However using files plus wet/dry carbon paper is time consuming.

I therefore have two questions to ask

1. Does anyone know of a machine with appropriate accessories to clean intricate metal without deeply scoring the soft copper?

2 Does anyone know of a chemical to clean off the blackening caused by the soldering?


Craig Humphreys
designer - Enfield, Middx, United Kingdom


? Could you give us a scope for the size of the pieces you are doing?

Marc Banks
- Elizabeth City, North Carolina USA


Q. The ends of the radiators we are cleaning range from 15 mm to 22 mm in diameter, of which there can be up to 12 in a single piece. These are affixed to another copper tube being spaced at between 20 mm to 25 mm intervals along its length. Hope this helps.

Craig Humphreys [returning]
designer - Enfield, Middx, United Kingdom


A. I think that this is going to be an experimentation thing, do up some pieces from scrap you can test on. Try a NON-DILUTED solution of muriatic acid to see if it will eat the black residue off, afterward passivate the surface with either lots of water or water and just a touch of Baking Soda . The metal will oxidize up again, but at this point I would suggest a bath of 5% citric acid. Dip and see if it cleans it up.



Be careful when using acids, they are corrosive, they give off fumes, and they can severely damage respiratory functions. That said, give my suggestion some thought, ponder if you have similar (but less dangerous) chemicals available that will do the same.

Marc Banks
- Elizabeth City, North Carolina USA

We merged some threads on this page. Please forgive what may look like disrespect towards earlier responses; they probably weren't there :-)

Brightening of copper radiator without harming solder


Q. Dear sir,
I am working in the field of metal treatment. I want your guideline for cleaning or brightening of radiator which is copper based without any proprietary formulation. Basically radiator is copper based, during process of soldering and other heat treatment radiator gets corroded or say tarnished strongly sometimes gets green. I have tried nitric and sulphuric based pickling but problem is there that soldering also get affected. so tell me any process which overcome such problems

Shitesh Thakur
radiator manufacture - Mumbai


A. I've used d-rust-it before and it works well on copper corrosion and it is non-hazardous too!

Howard Phillips
- Corning, New York

We merged some threads on this page. Please forgive what may look like disrespect towards earlier responses; they probably weren't there :-)

High thermal emissivity and thin coating needed

October 5, 2010

Q. Hello, I'm looking for advice on what the best finishing would be for a large passively cooled copper heatsink/radiator I've constructed, in order to maximise heat transfer to the surrounding air. Here's pictures and a link for what it looks like:

55866-1 55866-2

I'm looking for a finish for copper that will has a very high emissivity to increase heat radiation and is a thin coating so as not to decrease conductive heat transfer from the copper to the air too much. In terms of physical properties it needs to ideally not easily flake off when handling the large, heavy heatsink/radiator, but other than that doesn't need to be particularly hard-wearing. Ideally the finish will also colour the tin solder the same or a close colour.

Is there is a tried-and-trusted finish used for passive-airflow copper heatsinks/radiators?

So far I have come across either Cupric Oxide (Ebonol C) or Blackening with Liver of Sulphur as possible treatments, but I can't find any information on the emissivity or likely thickness of these coatings in order to judge which would be better, or if there is a better alternative. Any help would be much appreciated!

Dr Tom Gravgaard
Hobbyist - Margate, Kent, England

October 27, 2010

Q. Surely someone must have something to input? That's a bit disappointing.

Dr Tom Gravgaard [returning]
- Margate, Kent, United Kingdom

October 26, 2010

A. Hi, Tom.

Ebonol C is proprietary process chemistry offered by Enthone, and I'm pretty confident that they will have all the numbers you are looking for. A more casual chemistry, like liver of sulphur, is not likely to offer the consistency and robustness of a proprietary like Ebonol C, which has been a successful commercial offering for 50 years or so.

Sorry for the lack of responsiveness but unfortunately most of us have no idea what this thing you are building is, and it's not immediately apparent even from the dozens of pages of construction details you have so lovingly put on line. As I read your forum, and looked at people's avatars of racing slicks and their tag lines about their high-performance cars, I originally thought this was about car racing. You obviously are passionate about your hobby, and we are very happy that you are moving the technology forward, but most of us don't have the hour or two to study your project and fully appreciate what it's about and what its needs are. Personally, I post about a hundred inquiries per day on this site and am lucky when I have 5 minutes to think about a reader's project. Sorry :-(

Do I correctly understand that your project is about providing fan-less, pump-less cooling (water cooling?) to a high performance computer? Although the CPU gets hot, does this water cooling system really get hot enough that emissivity plays a significant role in the cooling compared to convection? The pictures are taken outdoors -- does the computer or its cooling system actually stay outdoors or does all the heat have to be absorbed into a room? I see a vertical aluminum or stainless steel mounting plate in your second picture -- what kind of stuff get mounted on this? Does the whole computer go here, and the cooling system is the outside frame?

It's unlikely that you could successfully electroplate this assembly. Electroless nickel plating might work but would be terribly expensive. You might be able to immersion tin plate it. I doubt that hot tin dipping would achieve much. I think you are on the right track with the Ebonol C. Regards and best of luck,

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

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