White Bronze Plating: an alternative to nickel

A. Hi cousin Hamza. White bronze is an alternative to nickel, often used on jewelry and similar items to provide a bright plating layer while avoiding possible exposure to nickel (which can cause the wearer to suffer 'nickel itch'). White bronze involves simultaneously depositing 3 metals -- which is a difficult trick because the metals have different electrochemical potentials so only the most noble 'wants' to plate out, the other two 'want' to stay in solution. So the metals have to be 'complexed' so that they are no free ions in solution. Some suppliers offer proprietary processes for the purpose.

This page offers a good intro to the subject and useful vocabulary and links for further research; and if you have specific questions I think the readers will be happy to try to answer them for you.

Luck & Regards,

A. Hi again Hamza. Brenner's "Electrodeposition of Alloys" [adv: this book on Amazon, eBay, & AbeBooks] includes 6-pages specifically on copper-tin-zinc alloys (Chapter 18.2), plus discussions on 6 other bronze-like ternary alloys, as well as more than 1300 pages on the general theory, practice, and problems involved in alloy plating. Try to get access to a copy.

I have to mention this to not mislead other readers: white bronze plating is usually done from commercially available proprietary solutions, not home-brew mixes. You're certainly welcome to pursue whatever you wish, but developing a robust white-bronze plating bath sounds like the work of many months, and possibly years. Good luck!

Regards,

A. Put 0.001 inches on it, and the jewelry will show up in antique shows 50 years from now. Put 0.00001 inches on, and like Broadway Gold, it will be the first thing to turn green in the spring.

A. Hi, Liz. White bronze is a substitute for nickel and will often prove acceptable. And if your product is jewelry, it addresses the issue of nickel allergy (leachable nickel is not permitted on jewelry in the EU).

But "environmentally friendly" without agreed-upon metrics is an empty buzzword, and I seriously doubt that white bronze is more environmentally friendly than nickel by any metric :-)

Due to relentless environmental pressure to reduce "environmentally unfriendly" phosphatizing, the world now suffers needless multibillion dollar annual corrosion, a colossal waste of energy & resources, and a complete lack of sustainability. Millions of tons of steel is no longer phosphated although we've known for 60 years how vital it is. We now mine, smelt, roll, fabricate, paint, package, sell, use for a short time then scrap (with transportation between each step), countless tons of steel every 2-3 years instead of the 20-30 years it used to easily last when properly phosphatized. We saved a ounce of phosphate at the cost of a ton of steel.

Please try to tell us what comprises "environmentally friendly" to your mind and then we can try to answer better whether white bronze is an environmentally friendly alternative to nickel. Good luck.

Regards,

A. Liz, you are in the heart of the jewellery trade in the UK. There are numerous organisations within 10 minutes walk of the city centre that can answer your problems and give you a huge insight into the metal finishing industry. Try talking with the Institute of Metal Finishing on Holloway Head, or the Metal Finishers Association in Vyse Street. There is also the Jewellery Manufacturers Association (I think in Vyse Street) and there is the College of Jewellery and Design (University of Central England, NOT Birmingham or Aston!)
White bronze is being used as a barrier layer in jewellery and other parts where nickel is banned. It does work well and is very effective. However, there are other alternatives, depending on what you are trying to do. If you can tell us what you are doing, there will be more help, but tap into the knowledge of your local experts first! Sorry to be so negative, but do the groundwork first and then come back and see what we can offer.

A. White bronze should be a good choice because it looks like what you are currently using, Liz; and it is widely used in jewelry, so there will be ready commercial sources ... although zinc plating would be an obvious answer if aesthetic enough for you.

Many people have skin allergies to nickel, but I would not call it "toxic". Electroformed nickel is used in stints and other items implanted into the body, for example. Hopefully if you or I ever need a stint it will be reliable electroformed nickel not white bronze :-)

Regards,

A. Liz, I am only trying to second guess what you really want - barrel plating is relatively easy to do, but you are limited to metals and alloys that can be electrodeposited from aqueous solutions. However, there is technology around that uses a barrel plating concept but with PVD/CVD type equipment. The people doing it in the UK are Teer Coatings Ltd in Droitwich - well worth a quick 'phone call and chat! Have a look at their website.

A. Hello Robert,

The corrosion resistance of White Bronze will depend on the base metal condition (Ra values) & the porosity of the brass in addition to the porosity of the Plating.

You can increase the corrosion resistance by plating two layers of White Bronze in different Chemistries, or adding a topcoat of Tin-Nickel alloy over the White bronze.

A. Hi again,

Sorry for the late response, I don't think it's necessary. I recommend a minimum 3 micron coat of bright acid copper plating directly over the brass before any other plating instead.

A. Hello,
2.5 microns will be fine. I'm sure your plater will know what chemistry they will use that will coat and seal the surface of the Zn die-cast parts before the white bronze plating.

A. Hi Sunny. The voltage required for electroplating is primarily related to the solution resistance, which in turn is primarily determined by the anode-cathode spacing and whether you are doing rack or barrel plating. For jewelry plating 3 volts may be enough, whereas 12 or even more might be required for high production barrel plating.

Regards,

A. Hello niloofar

I hate to be the one to tell you, but typically once the tin drops out of solution in alloy plating, the bath is most likely considered dead. The tin drops out of solution because it oxidizes. Once oxidized the solution is [un]able to redissolve it easily without destroying other components within the bath.

The most common reason tin drops out of solution is through aeration. This is usually through the use of air agitation in the solution (don't use air; use eductors for solution mix) or the pump is pulling in air and mixing it with solution.

There are a wide range of other reasons for tin to drop out however that is dependent on the chemistry of bath you are running.

Hope this helps!

A. Hi Niloofar. Despite the bath being analyzed, metallic or organic contamination seems very likely to be the cause. If you can e-mail a pic of a Hull Cell panel to mooney@finishing.com for posting here, readers can often make a highly educated guess as to the problem. Good luck,

Luck & Regards,


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

A. Hi Dhirav
Tank plating solutions are usually too drippy and watery for proper pen plating. Do a couple of lab experiments, thickening the solution with barium sulphate or maybe fumed silica to see if the solution still looks good and is thick enough. I'm not sure whether you can get the right alloy to deposit or not.
Luck & Regards,


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

A. There will be black spots because the alloy is not correct. Look at your alloy. Try high amperes first. The stain will disappear.