eboireau

Re: Silver/Rhodium tips?

Hi everyone,

I was wondering if anyone had any tips for plating Silver w/ Rhodium flash.

substrates are Al, Brass and copper/brass wledments.

I think I have my process down, but any suggestions or Tips would be great!!

Eric Boireau
H. LaRosee & Sons, Inc.

Eric Boireau
H. LaRosee & Sons Inc.
Hudson MA

skelton

Re: Silver/Rhodium tips?

Yo Eric!!! Greetings from Charleston...thanks for the posting.

I could either recite a book on plating on the list of substrates you mentioned you are plating....or you could maybe purchase one....but I think the most important part of your question is plating Rhodium over Silver.

I can honestly say that I am blessed to have spent a major part of my metal finishing career, learning and experimenting with different techniques of how to plate this, and how not to plate that, etc.....

The one key step in plating Rhodium is to go into the Rhodium bath "live". What do I mean when I say, "live"? You need to be able to initiate the DC current to the cathode rod (parts) prior to the parts entering into the plating bath. This will decrease the potential for passivation of the undercoating, in this case, silver, but in most cases, nickel, which is a very passive coating. And another helpful hint is to expedite the transfer process from the silver bath to the Rhodium bath, to not allow the pre-coat to become passive. Which, may not necessarily happen with silver, unless left out to dry and tarnish prior to the rhodium process.

And always spend some time to calculate your surface area and be certain to apply the most efficient level of DC current (asf) to achieve an optimum plating thickness, and of course, a quality finish.

I hope this has been helpful....pls let me know if you have any more questions.


Skelton, hOST
FinishingTalkLive
www.finishingtalklive.com

skelton's Website

eboireau

Re: Silver/Rhodium tips?

Great Advice!

Aluminium is seeming to give me the biggest fits, as everyone knows plating on Al is an artform more than a science. heres my Process...

Clean: Etch & Nitric Acid Desutter
Double Zincate: I always double dip
Electroless Nickel Flash: for a uniform base
Cyanide Copper Strike: for activation/reactivation
Bright Acid Copper plate: for that glossy shine
Cyanide Silver Strike
Cyanide Silver plate
Rhodium Sulfate plate

I got my running around down pat, 3 laps around the shop for 1 load of no more than 5 "small" pieces. MAYHEM

As of now, Im bucket plating the rhodium because of the unbelievable cost of rhodium sulfate!

Eric Boireau
H. LaRosee & Sons Inc.
Hudson MA

NANDKISHOR

Re: Silver/Rhodium tips?

how does nitric acid passivate stainless steel ?

RhodiumDoctor3

Re: Silver/Rhodium tips?

Eric, 

Skelton is on the right track with Aluminum; it is not autocatalyic, and takes extra steps to make it ready to plate, and he is very right about the passivation issue.  I'd like to add  some suggestions  about plating Rhodium over Silver and how you can easily CHECK to see if your parts are ready to plate.     Firstly, we are Davis K, a 35 year old manufacture of Rhodium, and my new customers constantly have problems with plating over Silver.   Here is one trick 1: 

Check for Passivity (readiness, or lack thereof!)  otherwise known as : the WET test:   Take a standard brass hull cell, and plate it with Bright Silver.  This is your test coupon, keep it around.  Run this test plate through your cleaning and activation process, up to the point where it will get Rhodium plated.  Dip it in clean water.  Does the water "sheet" (stick to) the whole plate, or does is gather in droplets?   If it doesn't "sheet" uniformly,  its NOT ready to plate, and niether would your subject part.   If you are not using an acid pre dip, introduce one,  5 to 10 % dilution of technical grade sulfuric, 2 good rinses in DI water, and you should be ready to plate. 

Trick 2.   You are cleaning like a demon, doing everything right, and you can plate a gold sample perfectly in Rhodium, but you still can't get good results with Silver.   If you can pre plate with Nickel, perfect, do that.  Should eliminate your issues.  If you can't, use Palladium, its a perfect barrier between non noble metals and Rhodium (it doesn't level anywhere near as well as nickel, but its great for Jewelry applications where nickel can't be used)    

Lastly , NEVER put Brass, Bronze, or other non noble metals into your Rhodium Bath!   If you have other issues with Rhodium, feel free to post or contact us.    glennt@davis-k.com