Hard Gold Plating Problems & Solutions / Q&A's

A. Safranek's book "The Properties of Electrodeposited Metals and Alloys" lists numerous options.
For pure gold, a sulfite bath was the hardest. Alloys of antimony or copper or cadmium or nickel in the range of 20 % were very hard relative to pure gold. Temperature and pulsed current can be used to make it harder also. If you are looking to do the plating, I would spend the money on the book.

Q. Thanks James.

We produce medals & badges for sporting organisations and schools from lead alloy castings. We currently use what I think is called "flash gold", potassium gold cyanide & gold conducting salts. Anything harder would give us an edge. I have access to many books, practical advice is what I need. Please.

A. Flash gold refers more to the thickness of the gold plate than to the type of plate.

The "formula" you mentioned is one that has been used for years for gold plating.

I am going to assume that your surface only has to look like 24K gold. I have done a little plating with a proprietary 10K gold that looked very close to 24K.

Since your email indicates that you are "down under", it would appear that you are stuck with whatever you can get from the platers that you have access to.

You asked for "hardness". The referenced book lists dozens of formulations with their respective hardness as well as the source document that the data was obtained from. I would say that that was more valuable than what two or three gold baths an individual might have used. Alloy gold hardness can run well over 10 times pure gold hardness.

A. Hi Daniela. I'm not on expert on contact design, but I haven't heard of any advantage to plating silver between the nickel and gold, and I would foresee the disadvantage of the gold and silver diffusing together into a less satisfactory alloy.

Hopefully an expert will correct me, but I think gold on nickel is ideal.

A. Gold will adhere well to Chromium and tend to be harder in thin films with Chromium under the Gold. We also alloy other metals with Gold in situ by co-evaporation. This can harden the surface substantially.
You can also use Gold alloys which are already made with hardening metals.

A. Hello
There is no or very little influence of nickel plating in regards to hardness of gold. The hardness depends only on the composition of the electrolyte which influences the deposition of gold.Surprisingly while studying hard gold we have found that there is also very little difference in hardness in regards to thickness of the gold deposit. Gold alloy deposit electrolytes that deposits 200+Vickers hard gold alloy have been developed. What is the hardness you require.

A. Hello, Lira. James Watts summarized that, of the pure golds, the sulfites were the hardest; but he also clarified that alloy golds are much harder than pure golds. Do you need pure gold or alloy gold, or don't know yet?

The book that James suggested covers all of the gold plating processes, so some solutions are cyanide based, some are acid gold cyanides, some (like the sulfites) are cyanide-free.

One recommendation which may not have been apparent is that you purchase gold plating solutions from specialty vendors like Technic, rather than try to formulate your own -- because such suppliers have decades of formulation experience, patents in the area, and expensive instrumentation for analyzing your solutions that you may not be able to afford yourself. Although some researchers formulate their own gold plating solutions in order to study them, I've never known a plater or a jeweler who made their own because it makes little economic sense.

What other kinds of recommendations are you looking for please--other gold plating books? "Gold Plating Technology" by Reid and Goldie is a very good one.

Best of luck!

A. Hi Jeanne,

My reply as below:

(1) Hard gold usually refer to alloy gold plating like gold cobalt or gold nickel which hardness is higher than soft gold (pure gold).

(2) Besides hardness increase, the metal (like nickel or cobalt) co-deposit in alloy gold usually serves as a brightener as well to increase alloy gold deposit brightness to certain extent.

(3) Brightener (inorganic or organic) can function as grain refiner (improve brightness), improve thickness distribution by slow down deposition rate at high current density and minimize burnt deposit at high current density.

(4) Usually soft gold provides better solderability than hard gold. Several microinches is good enough to preserve nickel solderability. Too high gold thickness may reduce solderability as more difficult for molten solder to dissolve gold deposit and form intermetallic layer (solder joint) with nickel. As soft gold with low thickness is preferred, gold brightness is not a big deal.

Regards,
David

A. Good day Noah.

I, too, am having a problem with my gold bath.
It is an E-56 bath which uses arsenic as the brightener.
The valency does change over time.
The bath is minimum 5 years old, with little demand on production.
The brightener consumption is well over recommendations, @ 0.2-0.3% BV per load.
I have now 90 ppm arsenic, 2 ppm nickel, BDL copper, 9 ppm iron.
It is not an organic issue, as carbon does not have any effect.
baumé @ 15, pH @ 5.75, temp. @ 127 F, Au @ 1.25 tr.oz/gal.
The efficiency is now @ 50%, due to the arsenic, and the hardness is being compromised.
I am plating 4 hours to reach 0.001" @ 40 mA per piece,9 pcs.
Tank volume @ 8 US gals.
I have no other recourse than to replace the bath.
I do know there are lead based brighteners which can provide the brightness and thickness, but I would need a deviation from the engineers.
One engineer will say the beaker is half full, the second will say it is half empty, and the third will say the beaker is twice the size as it should be!

Hope this is helpful.

Regards,