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How to measure amount of Gold used and left in the plating bath?

September 17, 2021

Q. Hello All,

We have started new gold plating line and procure gold (Troy Ounces) in powder form. The gold received in powdered form is measured to verify the received quantity is correct and is mixed/dissolved right away and poured into the gold plating tanks (no storage of gold allowed due to security).

We gold plate parts (mostly Soft gold and some case hard gold) as per ASTM B488. The question is how are able to verify the gold consumption and what is left over in the bath to ensure our inventory is ok.

Could any of you share best practices followed in inventory control on expensive metals like gold. In addition, how can we implement the consumption of gold in the Bill of Materials of part to be plated. Currently the BOM does not include chemical/ gold plating solution usage. I have plating surface area for 1 part, material type (copper) , qty to be plated etc. Any best practices or commonly followed guidelines in the industry, etc.

Thanks for all your feedback.

Regards
Elias

Elias Thomas
- Chicago, Illinois

A. Hi Elias. You know the surface area and the quantity of parts, and you presumably know the desired minimum or average thickness. So you should have a good handle on how much gold you are trying to apply, but with the complicating factor that plating thickness will vary across the part, which you can try to factor in by taking a number of thickness measurements.

You should add to that a record of the amp-minutes of power applied. If the plating efficiency were 100%, Faraday's Law would tell you exactly how much gold you plated based on those amp-minutes. A few experiments should determine the actual efficiency you are obtaining. You could probably include the amp-minutes or the amount of gold that equates to on your BOM.

Between calculating the approximate amount of gold which you are using according to the thickness, and calculating the amount you are using based on amp-minutes you should have a good handle on usage.

You can periodically analyze the amount of gold in the bath (see "Determination of the concentration of gold solution", thread 17144)

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2021

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