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topic 46268

Gold plating specifications - why is plating bright vs. matte?


A discussion started in 2007 but continuing through 2019

2007

Q. We have a part for which we specify gold plating for an electrical contact simply as "hard gold, 10 microinches". The substrate material is phosphor bronze, 1/4 hard.

The latest batch arrived from a new vendor with a matte finish instead of the bright finish that we have been used to. The plating thickness measured correctly at 10 microinches.

Questions:
1) Does a matte finish indicate that there may be something wrong or with the plating process that was used?
2) Is it usually necessary to specify "bright" or "matte" finish?
3) Can someone suggest a more thorough plating specification that would cover all necessary information?

Thanks!

Matt Carson
engineer - Guilford, Connecticut


2007

A. Dear Matt,
I shall try to answer to your questions as follows:
Questions:
1) Does a matte finish indicate that there may be something wrong or with the plating process that was used?
GOLD PLATING ON ITS OWN DOES NOT GIVE A BRIGHT FINISH. THE BRIGHTNESS DEPENDS UPON THE BASIC BRIGHTNESS OF THE BASE METAL. FOR THIS USUALLY A BRIGHT NICKEL/SULPHAMATE NICKEL UNDERCOAT IS GIVEN PRIOR TO GOLD PLATING. CHECK WITH your VENDOR.THERE ARE MATTE GOLD FINISHES AVAILABLE. BUT IT IS GENERALLY USED FOR DECORATIVE OR VERY SPECIFIC REQUIREMENTS.
2 Is it usually necessary to specify "bright" or "matte" finish?
YES. BUT your REQUIREMENT IS ELECTRICAL CONTACTS. THERE IS NO NEED FOR MATTE FINISH. NEVERTHELESS NO MATTER.
3) Can someone suggest a more thorough plating specification that would cover all necessary information?
MATT: You SHOULD BE CONCERNED ABOUT THE HARDNESS WHICH HAS TO BE IN RANGE 160-200HV. IF IT CONFORMS TO THIS SPEC, I DO NOT SEE ANY PROBLEM. YOUR POSTING DID NOT MENTION THIS BUT ONLY SAID "HARD GOLD"! YOU MAY PASS THIS AFTER CHECKING THE HARDNESS.
REGARDS,

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




"THE" brush plating book:
Electrochemical Metallizing

by Marv Rubinstein
from Abe Books
or
info on Amazon
or
see our Review

July 18, 2011

Q. I am in need of plating some idols in gold. Is it cheaper to do it myself using brush plating method (the largest is 18 inches high) or should I give it to a professional plater?

RFQ: If I am doing brush plating, where can I get the kit in India and detailed instructions? Suppliers can mail me.

Sankara Menon
- Cochin, India
outdated


July 19, 2011

A. Hi, Sankara.

It is usually faster, easier, and less expensive to do tank plating unless there is a specific reason to do brush plating. In the case of gold plating, where labor is a much smaller part of the total cost because of the high cost of gold, sending it to a plating shop may save money rather than cost money.

Regards,

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



How is this watch dial finished?

June 22, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi all,

I'm wondering what is involved in finishing brass (I presume it's brass as this is the standard dial material) to make it look like this Nomos watch:

46268

The manufacturer's website mentions plating with gold and silver, and 'galvanising' but it's a much softer, more matte finish than plating I've seen before.

Does anyone know how it's done?

Lewis Thomas
designer - London, UK


June 2015

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

A. Hi Lewis. We appended your inquiry to an earlier thread about matte gold plating which should offer you food for thought. There probably is no bright nickel plating below the gold -- perhaps dull nickel. There might also be an ultrafine glass bead blasting. Obviously we can only talk in generalities about how such things are usually done, not how Nomos actually does it, as we must be careful to avoid crowd-sourcing industrial espionage :-)

Another thing is that various colors of gold are available for watch plating (achieved via different percentages of alloying metals).

Usually faster progress will be made towards getting helpful answers if you explain your own situation. For example, dull nickel plating or alloys with a lot of non-gold may be no problem for watch dials sealed behind crystal, whereas adopting these answers to other product lines might be highly problematical in terms of nickel leaching, tarnishing of low alloy gold, etc. There is little concern about corrosion or leaching when components are sealed in a waterproof case, but the plating on those watch hands might not fare well if exposed to the world :-)

Regards,

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



Gold plating from tetrachloroaurate [AuCl4]

October 8, 2018

Q. My question is regarding brightening additives for decorative plating.

1. The article below shows some additive mixtures, but only for Potassium Gold Cyanide. Would it be possible to use the same mixtures for Tetrachloroaurate (Gold dissolved using Aqua Regia?)

2. Is a nickel underplating enough to obtain jewelry brightness, or do you need have the additive mixture?

http://paperity.org/p/3954099/bright-gold-electroplating-solutions

Kevin Mac
Gold Plating - San Jose, California, USA


October 2018

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

A. Hi Kevin. Reid & Goldie says that KAuCl4 was considered as far back as 1845 by Elsner, but it does not otherwise address it in the whole 630-page treatise. I find no other obvious reference to gold plating from AuCl4 in my plating library and I've personally never heard of it :-(

Best of luck to you, but I think the chances of successful plating from such a solution are nil regardless of what additives you employ. Please explain what motivates you to try such a composition. Thanks.

Regards,

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


October 11, 2018

thumbs up sign Thank you ted. I figure it would be nice to have a non-cyanide solution because of the prolonged exposure side effects; it's a big industry and regulations are getting more strict against working with these chemical.

Kevin Mac [returning]
Gold Plating - San Jose, California, USA


October 2018

A. Hi Kevin. Not to discourage further research in any direction you wish to take it, my understanding is that gold sulfite baths are the only production-viable alternative to cyanide.

Regards,

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


October 15, 2018

A. Hi Kevin
I have seen gold chloride baths used in commercial refining. The deposit is very pure but the quality of the plating is rubbish.
I know of no long term effects of cyanide. At sub lethal levels, the body has several mechanisms for eliminating cyanide which is good because cyanide is present at low levels in the environment and even some foodstuffs.
In any case, plating baths based on gold potassium cyanide contain very little free cyanide.
I agree that the safety community tend to be paranoid about anything associated with the C word but this is largely based on ignorance.
We understand cyanides very well but the same cannot be said for any of the proposed alternatives.
You can find considerable factual detail at
https://www.academia.edu/10635761/Cyanides_in_Metal_Finishing_Risks_and_Alternatives

geoff smith
Geoff Smith
Hampshire, England



June 4, 2019

Q. Hello there. Nice to meet you all of you. You can call me Phu. I am final year undergraduate student who is doing project with this gold plating on copper and brass using non cyanide bath for decorative applications.
My question is what is the use of brighteners in the gold plating solution? Does this not make the gold plate bright enough? Do I still need to plate bright Nickel layer first in order to have a bright finish of gold?

Mya Phu Pwint Thit
Yangon Technological University - Yangon, Myanmar


simultaneous June 4, 2019

A. A good bright gold solution will plate bright on your bright brass substrate without using nickel but if your gold solution does not contain brightener it will plate dull on your bright substrate

Neil Bell
Red Sky Plating

supporting advertiser
Albuquerque, New Mexico
red sky banner ad


June 5, 2019

A. Hello Phu,
The purpose(s) of gold brighteners can vary from what the gold plated item will be used for. Because the gold plated layer is generally thin, the actual gold deposit brightness depends on how bright the underlying metal is. This is why bright nickel is used before gold plating in decorative applications, with the exception of plated jewelry which comes in contact with the skin. White bronze and palladium are used a lot in this case. Many of the hard acid golds contain brighteners such as cobalt, nickel, silver. These brighteners dictate the purity of the deposit, color, hardness, alter the grain structure of the deposit and increase the current density range. Color golds don't have brighteners per say, but alloy metals to achieve color and karat. The use of a barrier plate such as nickel will also prevent metals such as copper or brass migrating into the gold causing tarnishing and corrosion. Good Luck with your studies.

Mark Baker
Electronic Plating - Winston Salem, North Carolina USA


June 6, 2019

thumbs up sign  Thank you guys.

Mya Phu Pwint Thit [returning]
- Yangon, Myanmar



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