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topic 50905 p.1 of 2

Gold sulfite bath plates red-brown instead of gold color


A discussion started in 2006 but continuing through 2019

2006

Q. Hi all, I was wondering if someone could help me. I have heard that it's possible to gold plate jewelry without the use of cyanide, using something a lot less toxic and an anode instead of the gold in the solution. I would appreciate any feedback.... thanks

Chris Kalogeras
opal trading - Adelaide, S.A., Australia


2006

A. Hi Chris. Acid gold cyanide is not nearly as toxic as sodium cyanide itself, but there are also gold sulfite and other gold plating baths which are cyanide-free.

I am not aware of any gold plating bath that uses gold anodes, but this is probably not due to technical limitation so much as the general impracticality of buying and safely securing hundreds of pounds of gold.

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


simultaneous 2006

A. What's the big deal with cyanide, anyhow? It's used by the ton, hot enough to be molten, in some metal heat treatment processes.

If you're using a solution of a cyanide in water don't drink it just as you don't drink any other poisonous liquid, and don't add excess acid to the solution just as you don't indiscriminately mix other substances.

Bill Reynolds
Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.



2006

A. You can use next solutions:
1 gm gold chloride
70 gm sodium phosphate
2,5 gm sodium sulphite
1 lit water
stainless steel anode,only grease and oxide free objects can be plated

Or you can use ferrocyanide based solution (0,5% of potassium cyanide toxicity):

2,65 gr gold chloride
15 gm potassium ferrocyanide
15 gm sodium carbonate (water free)
1 lit water
Stainless steel anodes
Dissolve ferrocyanide in boiling water; when dissolved add carbonate, and when it is dissolved add gold chloride. Boil it 30-180 minutes, add evaporated water, filter it and you can use it. Good luck!

Goran Budija
- Zagreb, Croatia



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2007

Q. Hi,
I am involved in a research on gold plating for a Temple project in India.
I am radio electronic inventor, and can deal with chemistry as well.
We will have to gold plate a big area of the roof of the temple here. But it will be very difficult to control the quality of gold plating here in India if we order some. So, I am looking for Your help and advise for how I can prepare my own chemicals for electroplating from metallic Gold and any other chemicals (all available here in the market)
But I have heard that cyanides are very poisonous. So, I would prefer Chloride or DiPhosphate of Gold.
Can it be prepared? It will be also cheaper, I believe.

Hope this meets You in good health.

Alexander [last name deleted for privacy by Editor]
inventor, monk, minister - Vrindavan, UP, India


2007

A. Hello Alexander. I don't really agree with the premise that formulating your own gold plating solutions is necessarily more economical; and I think it may be difficult to control the quality of the gold plating solution if you don't order it from a qualified supplier (although a researcher in an advanced facility with state of the art instrumentation and good access to technical info has a fair chance of preparing an acceptable gold plating solution).

And when dealing with precious metal plating chemistry, the precious metal is so expensive, and waste becomes so costly, that any value-added cost for the process chemistry is marginal. Your money, your choice, but personally I'd pick a brush plating supplier and order their equipment and chemistry.

Ideally you should get some plating textbooks, but if that proves impossible then you can view the digital version of the Metal Finishing Guidebook on-line, which has some formulas for gold plating baths as well as some instruction. Best of luck.

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


2007

A. Two cyanide free plating formulas (both work as ordinary plating solutions but can be used as brush plating solutions):

No 1:
1 gm gold chloride
75 gm sodium phosphate
2,5 gm sodium sulphite
1 lit water
stainless steel anodes

No 2. 2,65 gm gold chloride
15 gm potassium ferrocyanide
15 gm sodium carbonate
1 lit water
stainless steel anodes,
(dissolve ferrocyanide in boiling water,when dissolved add carbonate, then add gold chloride. You can make your own: dissolve gold in aqua regia, boil 1,5 -2 hours; when cold, add evaporated water and filter it). Test it first on some metal scrap.
Hope it helps and good luck!

Goran Budija
- Zagreb, Croatia


A Complete Treatise On The Electro-Deposition Of Metals ...
from Abe Books

or

^-- A reprinting of a 1924 book.

2007

A. Alexander,
I agree with Mr. Mooney. Trying to develop your own chemicals and process just to find out something is going wrong over and over again with such an extremely large and complicated project, especially when one of the most expensive metals is involved, may prove to be not just a technical but a financial disaster. Get professional equipment and products and expert advise.

Mr. Budija
Regarding the formulas given, do you know what their pH range is? Is there any pretreatment necessary to obtain adhesion or to avoid attack to, or diffusion into the substrate?

Guillermo Marrufo
Monterrey, NL, Mexico


2007

A. Dear Guillermo!
These two baths are old 19th century formulas and both work -- bath no .2 (from Langbein's handbook, but this type of formula is much older/1844./) can be used on brass, copper, nickel,and iron, tin and pewter without any special pretreatment (oxide and grease free surface). That's all I know.

Best and simplest solution for that job is leaf gilding.
Hope it helps and good luck!

Goran Budija
- Zagreb, Croatia


October 28, 2009

A. I don't know about the use of stainless steel anodes, I would figure that it would cause a cementation of gold chloride into metallic gold. I would recommend a platinum electrode for the low overpotential.

Derek Blais
Graduate Student - St-Lambert, QC, Canada



June 1, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. CYANIDE FREE BATH?

Hi I just came across this forum. I am looking for cyanide free bath recipes for gold electroplating. I know there are some products readily available, but I did the math: even on ebay if you calculate the cost per gram of gold content costs least twice of the regular gold price. Plus shipping. Some companies do not ship to my country.

So I decided to do it myself. I studied science like a quarter of a century ago, I am not afraid of chemistry.

Here are the choices:

1) Cyanide containing bath solutions - out of question

2) Potassium ferrocyanide+Potassium carbonate+gold chloride
I know ferrocyanide is not very toxic, BUT once you prepare the mixture I think you exchange the Fe ions with K ions , you filter the iron oxide and you will have a KCN solution or least K[Au(CN)2] . The product is just as toxic as Type 1. Does anybody know the equation?

3) Gold sulfite
I did some research and I see it is not easy to produce at home

4) Fizeau's solution: 1g gold chloride + 4 g sodium hyposulfite in 1 litre of water. Did anybody try this? pH? Temperature?

5) :
1 gm gold chloride
75 gm sodium phosphate
2,5 gm sodium sulphite
1 lit water
stainless steel anodes
Did anybody try this one? pH, temperature?

6)
Chloride base bath:
gold chloride.......25-40 gm
HCl(1,19 gm/l)......20-50 gm
sodium chloride.....10-30 gm
H2SO4(1,84 gm/l)....10-20 gm
water................1 lit
temp.................70 °C 8-10 A/dm2
Who used this one?

7) Gold chloride itself. Some old books say it should work as well. What are the problems with that?

8) Any other CN-free options ?

Thanks a lot

Thomas Torok
- Toronto, Ontario, Canada



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



January 8, 2009

Q. We're running a small tank (4 gallons) of bright gold bath. We recently purchased a new bath. Always in the past they have worked fine right out of the bucket. This bath, first test piece, after 1-2 minutes in the tank (spec 3 ASF, good temp & agitation) looks a godawful reddish-brown, so I pulled it. I start checking, new bath is below spec on pH (8.6 vs 9-10), so I adjust, try again. Same thing, piece looks ruined after 1-2 minutes.

We keep working with the process and eventually find that a piece will look ruined at 1-2 minutes, but if we stay in the tank for 5-6 minutes it begins to brighten and ends up looking Okay. When the piece starts to brighten, the plating voltage drops from say 0.8 to 0.65 Volts (running a constant current supply at 200-300 mA, for 3 ASF)

I'm working with tech support but they've never seen this before. I've never seen this before, running the same process for 10 years. This is a sulfite gold with arsenic brightener.

Has anybody seen this kind of thing, know a probable cause?

Thanks,

Gerry Petencin
Plating manager / plater - Charlottesville, Virginia, USA


January 13, 2009

A. Gerry

Sulfite gold baths are very sensitive to voltage. I would check the anodes and make sure they are clean before you begin to plate and not covered by an insulating layer of sulfur or sulfite breakdown products.

Pat Mentone
Pat Mentone
St Paul, Minnesota


"Gold Plating Technology"
by Reid & Goldie
from Abe Books
or

January 14, 2009

A. Hi Gerry,
I think there is deficiency of initial brightener addition in the bath. Try adding 3 mls/ltr and see if there is any improvement. You may need to add up to 10 ml/ltr or more.
Please let us know the result.
Good luck

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India



January 26, 2009

Q. Thanks for the interesting replies. We're still working on this, our vendor is issuing an RMA for faulty product. Your comments, if we did a brightener add like that it would drive the bath way high on arsenic, per analysis done on this bath and spec. But a plater who used to work here with that process would have done exactly that (his personal approach was "always add brightener") and who knows, it might have fixed it? We have done small adds of conducting salt and brightener with no positive effects.

Comment on the anode is interesting too. We started with the "old" anode which did have a coat of yellowish stuff (sulfite or gold?), then switched to a newer clean anode set. We run constant current supplies and didn't note any unusual voltages or voltage drops in the system.

Do anodes have a life expectancy?

Thanks, Gerry

Gerry Petencin [returning]
Plating manager / plater - Charlottesville Virginia USA



Fighting sudden undesired plateup in sulfite-based gold plating bath (Techni Gold 25E)

October 7, 2009

Q. Hi everyone,

My name is Dominic Frutiger. I am with the Institute of Robotics and Intelligent Systems at ETH Zurich, Switzerland. It is an university and not industry, but my question might be general enough to be of interest to others.

We produce some of the currently most successful microrobots, i.e., little mobile agents that are only a few widths of a human hair -- video illustrating this:

For one part of the robot we use electroplated gold in high-aspect ratio trenches (e.g. 6 µm wide, 35 µm high, plating 25 µm of gold into it). So far we have been relying on Techni Gold 25E and it gives good results for a while, say 6 months or 20 wafers -- but then it invariably "fails". Failing here does not mean it stops plating. The deposits may still look nice and shiny. It just starts to exhibit significant plateup on photoresist walls which is really a show stopper for us (say 5 µm plateup for 8 µm of normal, smooth deposit).

We checked all the parameters and cleaned the bath. We added gold and other required ingredients. We are not aware of any pollutants, but then again that is hard to know. The supplier apparently has no further advice to offer.

Now we are clearly more like your garden shack type platers with little professional know-how when it comes to electroplating gold -- but there must be people out there that have experienced a similar problem (probably with the same product even) and that might be able to help with pointing us to say a particular leveling additive or a different product or with some other general piece of advice.

We are of course looking into different options and processes in the meantime that do not include gold. However, this is an important and expensive piece of equipment and it would be great to be able to "recover" it and make it usable for this particular purpose again.

Thank you
Dominic

Dominic Frutiger
microrobotics researcher - Zurich, Switzerland


October 8, 2009

A. Hi Dominic

A few ideas to work on --

Sulphite golds tend to be very sensitive to pH. I have seen an entire large bath "fall apart" and deposit all the gold on the bottom! More commonly there can be bridging of gold between adjacent conductors which was traced to cleaners trapped under masking tape leaching out to locally change the pH.

The photoresist could be a source of trouble. Positive resists are acidic in the exposed area. That is why they develop in alkaline solution. If the developing is incomplete, there can be local acidity. This is usually not noticed but you are working with very small dimensions.

So ... You need good pH control. If you are not familiar with pH meters you will need to learn to use one properly. The procedure in the plating industry is often dip it in and read. For critical work it is a little more complex.

Good exposure control and developing of resists requires thickness control, exposure step wedge, control developer chemistry, very thorough rinsing, etc.

It is also worth considering a drag in bath before plating buffered at the pH of the gold tank.

Hope this helps

geoff smith
Geoff Smith
Hampshire, England


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