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topic 5106

Tin Plated Parts are Turning Black

A discussion started in 2000 but continuing through 2019


Q. We are using many Tin plated brass components in our product.We are facing a problem of oxidation of this parts. This parts oxidize with in 2-3 months while storing. The surface of this parts becomes black. Tin plating of the part is our customer requirement so we can not change the plating. Would someone will give any suggestion to overcome this problem Thanks in advance.

Bahadur Singh Rathore
- Udaipur, Raj., India


A. Bahadur, Without seeing the parts it sounds like de-zincification of the brass. With zinc being anodic towards tin it will tend to migrate into the tin deposit over a period of time and cause the discoloration you are seeing. You will need a copper or nickel barrier layer to prevent this.

Rick Richardson, MSF
Dayton, Ohio


A. Black on tin plate is almost always caused by the sulfur in cheap paper vaporizing and tarnishing the tin. Wrap in the fine white paper that they use in department stores that sell silver and fine china. for longer term storage in a non air conditioned environment, store in plastic boxes--Tupperware--type in the USA.

For oxidation, we used to dip the parts in a solution of stearic acid dissolved in xylene. this was per some specification that I do not remember the name. Probably military or ASM. This will about double the shelf life of the solderability of parts.

James Watts
- Navarre, Florida

February 8, 2010

A. You need a copper layer between the brass and the tin to avoid migration

You also need a mild alkaline post dip

On top of that, if the solution is old it accumulates organic breakdown products. In this case you have to dilute or dump the tin plating solution

sara michaeli
Sara Michaeli sara michaeli signature
chemical process supplier
Tel-Aviv, Israel

November 13, 2011

A. This issue could happen on brass or other alloy contains zinc, because during the dipping process brass could easily form zinc-concentrated areas, which will restore the acid solution (sulfuric acid) back to sulfur during the plating process. The sulfur will gradually react with tin and form tin monosulfide which appears in dark color.

Pre-coating with copper for isolation between zinc and tin could prevent this issue.

Mike Gwo
- Xiamen, Fujian, China

Black marks on tin plated copper

September 26, 2010

Q. Very good morning to you all,
Actually these day we are facing black mark problem on tin plating surface in one of our products parts. Do any have an idea to clean that black mark problem? It's urgent -- please advise. We have tin plating thickness of 4-7 micron on copper.

Mukesh Vyas
engineer - Haridwar, India

Tin plated brass turned completely dark black

April 30, 2012

Q. I have terminals that have turned completely and uniformly black. Brass base material is 70% Cu, 30% Zn. Plating is a 4µ Cu flash with 8µ Sn.

I put 500 pieces from a 1000 piece bag in a bowl feeder with a clear plastic cover in our production line on Friday. They sat over the weekend under climate controlled conditions. They were all black on Monday. The remaining parts in the bag on the shelf were still Sn color.

We have run this process in this manner for many months with no issue. The plating supplier has never seen this issue. We cut and sectioned a part to confirm the Cu layer.

Is there any agents, chemical or otherwise, that would activate this process? Is the black layer an oxidation?

Our manufacturing area is very tightly controlled for contamination.

Any information is appreciated.

Thank you,

Steve Pugh
- Anderson, South Carolina, USA

May 2, 2012

A. Hi Steve.

"When you've ruled out the impossible, then, no matter how improbable, . . ."

Tin plated parts are subject to a darkening condition called fretting corrosion. Any chance that somebody accidentally left that vibrator on over the weekend?


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

May 3, 2012

thumbs up signHello Ted,

Our operator advised that the vibratory bowl and equipment was all powered down over the weekend so we ruled that out at first. We have done recreation tests. We are able to recreate the problem by leaving the vibratory bowl on for 48 hours. Somewhere along the line it was left on. The answer to your question is yes!

Thank you,

Steve Pugh [returning]
- Anderson, South Carolina, USA

Tin plated meat grinders turn black

November 4, 2012

Q. Why do tin coated cast iron meat grinders turn black? The better quality hand powered cast iron meat and all purpose grinders have traditionally always been hot dip tin coated. This includes the ones still made today in the orient and in Europe.

It is very common for dark spots to develop over the years until only a little bit of shiny tin is visible. I have always assumed the dark stuff was rust and the areas where it occurred were the spots where the tin had worn completely away, but the dark spots resemble the iron oxide one gets when one treats rust with phosphoric acid, which has me wondering if it isn't the tin itself, which has for some reason changed color. Also, I notice some areas where the tin has clearly been completely removed have normal reddish rust. Like iron oxide, this black stuff is very hard, and using Scotchbrite I have had no luck removing it (I don't want to use anything harder, for fear of damaging whatever tin is left),

The dark spots are sometimes a bit greasy feeling, and bead water, and other times dry, so dry that tiny chips will fall off on your hands if you rub it.

Anyone have any idea what the black stuff is, and whether there is any way to remove it or recover some of the tin that may lie beneath?

Kyle Morley
- Concord, New Hampshire, USA

Tin plating turns black after a few months

November 5, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,

I'm facing tin plating problems.

We do bright acid tin plating on copper lugs. For some reason they are turning black within 4-5 months.

We got a customer complaint of the material dispatched in August 2012

Please help me.

Jack Roman
Engineer - India

November 10, 2012

A. Hi Jack,

The problem could be due to tin tarnishing upon long storage and/or harsh storage environment (high temp high humidity, corrosive environment, etc). You may apply proprietary post dip (other than generic trisodium phosphate) after tin plating to create an hydrophobic protective layer on top of tin deposit against air/moisture contact.


David Shiu
David Shiu
- Singapore

November 16, 2012

A. Hi,

It's a migration. Use a nickel strike instead of copper.


Anders Sundman

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden

April 4, 2013

Q. Dear All,
We are doing bright acid tin on copper lugs and this are d results we are facing after certain period of time. Can any one help me to solve this problem as this is affecting me to loss of costumers?

dark spots on cast iron

Abhiraj Naik
Engineer - Mumbai, Maharahstra, India

April 8, 2013

A. Abhiraj,
It sounds like you're getting SnO or SnO2 forming from slow interaction between the tin plating and cleaning agents with a high pH (heavy in the OH group). This means that the plating was doing exactly what it was supposed to do, oxidizing so the metal underneath did not.

To sum up:
Hot + humid + high pH = blue black SnO

Tin(II) Oxide

If it's gone too far you may want to get them re-plated.

I don't think that recovering the tin from the plating is going to be cost or time effective. It's unlikely that you have more than 3 g of tin plated on any one grinder. Recovery would be a multi-step process involving various acids, reagents, and processing probably exceeding the cost of purchasing tin metal.

Ref: =>

Marc Banks
Blacksmith - Boone, North Carolina, USA

April 9, 2013

A. Hi,
It also could be tin plague. A tin deposit with no alloy in the tin deposit change from Alpha phase to beta phase in cold atmosphere and will dissolve.


anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden

April 12, 2013

Thank you all for your valuable response on my email.

Q. Can you please suggest me the remedies for such problems that they shouldn't occur again after tin plating?

Abhiraj Naik
- Mumbai, Maharashtra, India

April 19, 2013

A. Abhiraj,
If the parts are frequently exposed to moisture and aggressive cleaning agents I'd suggest paint or enamel. There are several 2 part epoxy paints that would probably do quite well for providing an additional moisture barrier.

Marc Banks
Blacksmith - Boone, North Carolina, USA

April 18, 2013

A. Anders has a good point - you may need a barrier layer, such as nickel. However, I reckon the tin has migrated into the copper and formed an intermetallic compound (Cu3Sn). This can be a very fast process and will increase in rate at elevated temperatures. The inclusion of a barrier layer will stop it.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

April 23, 2013

Q. We are currently experiencing uneven and low thickness and rough deposit of tin plating on Cu. Our additive is below the specs (122 ml/l target, actual 95 ml/l) for we have issue on out of stock primary rbm additive. In addition, we also observed Nickel on tin deposit from EDS analysis. Do you have any suggestion on containment action that we can do while waiting for the additive delivery? Also, how can we remove Nickel from tin plating bath if it will be proven at high ppm level? Thanks for your time and looking get your expertise regarding our concern.

Trisha Reyes
- Laguna, Phils

July 12, 2013

Q. Hello,

We make copper and brass parts for transformers. The brass used is 56 Cu, which is diecast to form components. The machined components are tin plated, sometimes with a pre coat of copper and otherwise with nickel. The parts are turning dark within as less as 2 days. The transformers are used in heavily polluted atmospheres.
Please advise on the coating thickness of tin and copper/nickel to prevent this, also if it is happening because of partly rough surface of the machined component?

Ratnmani Jain

August 26, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We are using some copper bus bars with nickel undercoat and top matte tin plating. In one batch we found that plated parts are getting blackish. I want to know the reason behind this issue.

silver turns black 5106-3  silver turns black 5106-4

Raghava Reddy
- Banglore, India

August 26, 2013

A. Hi Raghava. We appended your question to a thread which offers food for thought. There are many possible causes of tin blackening, from sulfur in the air or in the packaging, to fretting corrosion, to contamination of the plating bath, etc. We'd like to help you, but it is not easily dispatched without a lot of operating data. The plastic film and cardboard packaging is certainly a prime suspect. Good luck.


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

August 28, 2013

Q. Tin Plated Parts are Turning Black

We are using tin plating for aluminium components. We have a oxidation or immigration, the surface of the parts are coming black. The parts are in storage for 3 to 5 months. Would someone will give any suggestion to overcome this problem Thanks in advance.

- Juarez, Chihuahua, Mexico

August 29, 2013

A. Alkaline stannate tin brighteners will not "rinse" off, you must go back into a mild soak cleaner to remove the brightener film - if left on, the tin deposit turns black.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

August 30, 2013

Q. Finish of aluminium bus bar with nickel undercoat and top matte tin coated parts color differs from batch to batch and some parts looks like black instead of light grey.
Why? And how to control this?
How can we get uniform color in this kind of plating ?

Raghava Reddy
- Banglore, India

September 9, 2013

A. Hi Raghava,

The black colour could be due to poor tin grain structure (e.g. burnt deposit at high current density) or tin oxidation.

To get uniform tin deposit colour, you should follow supplier recommendation to analyse and replenish proprietary additives (e.g. leveller, grain refiner, etc) and to insert post treatment (e.g. neutralizer, anti-tarnish) and adequate DI water rinses after tin plating to ensure plating chemical residues are fully removed prior drying and tin deposit is protected from oxidation by anti-tarnish coating (hydrophobic coating).


David Shiu
David Shiu
- Singapore

November 27, 2013

Q. Hello all,

I've got the same problem with a Zinc diecast product which is plated with Tin over Nickel over Copper.
We use a reflow temperature of 240 °C.

After reflow about 40% of the parts turned brown.

If I want to put an anti-tarnish layer on, which layer I can choose as the best? Do you have brands and types?

Gerard Vervaart
- Hertogenbosch, The Netherlands

December 4, 2013

A. Gerard, Tin will form intermetallic compounds with copper, and nickel and I believe it will quickly diffuse into zinc. I believe that the interaction of tin on zinc is a way of producing tin and zinc whiskers at very fast rates, so there is certainly some adverse interactions going on. The rate of formation of the Cu-Sn intermetallic compounds is much faster than those for Ni-Sn and since you are flow melting at 240 °C - above the melting point of tin, the diffusion rates are significantly enhanced. I suggest you increase the amount of tin put down and reduce the time the substrate is held at an elevated temperature.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

December 9, 2013

Q. Hello Trevor,

Thanks for your quick response; indeed that is the reason we put first copper and then nickel as barrier between Zinc and Tin. Maybe increasing the tin layer is a suitable solution. Actually we are starting a trail run with a anti-tarnish layer after the plating operation. For your information, the connector is soldered by reflow which means that the max. temp of 240 °C is only a couple of seconds. I'll keep you informed about the test results if you are interested?

Gerard Vervaart
- Hertogenbosch, Netherlands

January 6, 2014

Q. I face high carbon and oxygen content on tin plated surface (with copper underlayer) by SEM-EDX analysis. The black area is unsolderable during reflow.
I used hot air blower and performed manual soldering; I able to re-solder it again.
The tin plating is matte tin.
Any possible cause for the black residue?

Vincent Loh
- Melaka, Melaka, Malaysia

January 7, 2014

A. Hello Vincent,
The 3 major causes for carbon to be present in the tin deposit is storage conditions, and excessive organic additives in the bath and bath impurities. Because you are using a Matte Tin Bath, you can pretty much rule out the organic brighteners. Are these parts stored at room temperature right after tin plating, up until the point of soldering? What about humidity and the general atmosphere where the tin plated parts are kept? Here is a test you can run... Plate the parts in tin normally. Be sure you have good rinsing and clean drying techniques. Wrap parts in sulfur free paper, or just a plastic bag and store in a room temperature environment. Wait the usual time before soldering. If you still have the problem, the tin bath should have a full analysis including metallic impurities. It would also benefit you to put a few carbon filters in your filter system for a few hours apiece in case you are dragging in organics during your plating cycle. Good Luck.

Mark Baker
Process Engineer - Malone, New York, USA

Tin plated pistons have black stains from storage

July 20, 2014

Q. Hi

Recently, I found that all the tin-plated (automotive) pistons stored in my warehouse have strange black stains. It appears as if they were all dipped in some solution and then left to allow dripping and drying.

Can anybody suggest me some remedy otherwise, all that huge stock will be a big blow for me.

Thanks in advance for the help.

Aamer Reza
- Lahore, Pakistan

February 8, 2015

Q. We are producing tin plated copper bus bar but I have problem that some areas turn black maybe after one day.
Last time we sent to customer he sent a complaint, as we do tin coating, and in next day we send it to customer: BUT WHEN HE OPENS THE BOX HE FOUND BLACK SPOTS ON COPPER BAR. So please anyone can guide me what to do?

ahmed ismail
- riyadh in saudi arabia

February 2015

A. Hi Ahmed. You posted your inquiry onto a thread with lots of hints about possible causes. But my first guess is that James Watts is right, that you are not using proper sulphur-free packaging. If you are, please try to frame your ongoing questions in terms of the suggestions that have been offered. Good luck.


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

February 20, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Tin plated (min. 5 µ) Al parts surface going dark in very short period; tarnishing starts in just 1-2 weeks. Process steps: Zincate + Cyanide Cu (max. 1 µ) + Tin (min. 5 µ)
Any suggestions about this problem? Many many thanks.

Engin Kalip
- istanbul-Turkey

Removing stannic ion fixed tin plating that was turning black, but now the bath is blue

May 18, 2015

A. Hi last time I used phosphoric acid to sediment all the stannic tin which causes the pieces to turn black ...

Q. Now I have good results but the color of the bath turned from yellow to blue -- is that normal?

capacho francisco
Ingezinc. - bogota,Colombia

Unknown Black Deposit on Tin Plated Copper Brazed Joint

October 21, 2015

BAg-7 56% AG Wire Solder

Q. We have a problem with an unknown black deposit only occurring on the bottom joint from where the part is hung when tin plated. All of the other sides of the joint are fine.This occurred equally on 5 joints that are on this part. It is a copper bus bar with BAg-7 braze alloy that was torch brazed. We have also seen this occur on similar products when resistance welded, using BAg-7. All parts have been quenched using an Isoprep 192 solution, rinsed in water, and dried.

The deposit is relatively easy to remove, but underneath is bare copper. We currently use a wire wheel to remove it and paddle plate the affected area with no problem.

BAg-7 Alloy is 56% Ag, 22% Cu, 5% Sn, and 17% Zn

Flux Used is Silvaloy Black Flux for Silver Brazing

When able I will add pictures.

Neal Gerus
- Monee

June 14, 2016

Q. Hi,
In FPCB, Tin plated on Cu.
Customer found dewetting issue & cross-section shows, kind of a corrosion in Tin layer.
Almost 50% of Tin thickness from outside has turned to black (not shiny) and rest is intact with Cu layer.


Please advise what could be that black layer which is causing dewetting during soldering.

Manju Penang
- Penang, Malaysia

October 2, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi there, I seem to be having a few issues with my tin plating process

1) What is the correct temperature to do the tin plating at?
2) Why is it that when the amperage is high, the plating tank/bath seems to create a lot of foam on the surface?
3) I am getting black deposits on the items being plated, is there any way to remedy this?
4) I have used chemicals from one supplier, however I have changed suppliers but the chemicals they use for tin plating is different, how would it affect the tank composition/chemical balance?
5) Our tanks were initially made up of only Atotech's chemicals, however they no longer have a branch in South Africa. Is there anyway that I can import the chemicals or find another distributor of Atotech's chemicals?

Thank you for your input, It will be much appreciated

Paul Calvert
- Cape Town, South Africa

October 2016

A. Hi Paul. We appended your inquiry to a thread listing some of the causes of tin plating turning black. As you can see, there are a lot of possibilities, some of which depend on the substrate and the type of bath.

Help us envision the situation by telling us whether you are rack, barrel, or strip plating; what metal the substrate is; the purpose of the plating (electronic parts, decorative, etc.); and what type of plating bath you are operating (MSA, bright acid tin, stannate). Thanks!

Mixing chemicals from two suppliers is a problem. I think you should find a distributor of tin plating processes in South Africa. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Striving to live Aloha

April 24, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Why black color marks are formed on the tin coated bus bars of the new panel board which is not yet energized?

irshad alam
abc - riyadh, saudi arabia

July 19, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My situation:HI!

I am a Plater. While doing tin plating, I am facing problem of blackness on brass terminal during Tin plating after tinning of 1-2 days.

Please give solution.

Rupender Juneja
Plater/Businessman - Gurgaon,Haryana/India

July 2018

A. Hi Irshad, Hi Repender. As you see, we appended your inquiries to one of several threads about blackening of tin plating. Please review the page and then ask any questions or explain the ways in which your situation might be different from what has been described. Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Striving to live Aloha

July 21, 2018

A. Dear Rupender,

The blackness over tin plating is called tarnish on the plated surface. After tin plating the parts must be neutralised by mild alkaline solution then good rinsing.

Hope it will help you,


P Karthikeyan
- Electronics City, Bangalore, India

Tin plated copper electrical work turning jet black

January 12, 2019

Q. Hi, we provide electrical engineering support to a nickel concentrate plant supplied by a high voltage outdoor switch yard. They introduced a new bio leach process which causes warm plumes of (they say HCl) but I think sulphuric acid or hydrogen sulphur. Anyways, in the space of only two months ALL the tinned copper overhead lines, copper busbars, silver-tin alloy connectors and such have turned jet black!

Reading the threads, it sounds like,a sulphur in air + humidity problem but we have no idea how the blackening may affect the reliability of the HV switchyard or how to treat the parts or if they are all replaced, how to coat the parts to prevent further problems.

Could anyone help me with this or even point me in the direction of the the kind of chemist expert we could use to investigate?

Kind regards, Tim

Timothy Edwards
Metro Power Company - Perth, Western Australia

August 4, 2019

Q. We have yet not got rid of this problem of blackness on tin plating.
We are providing nickel undercoat, still the problem is persisting.
If any ne has found a solution and seen the results practically, please share asap


Ratnmani jain [returning]
Metalcast - Delhi, India

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