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topic 6338

Rhodium Plating Solution


(2000)

Q. I would like to do some rhodium plating over gold.

The local jeweler uses a non-cyanide solution,

I have seen references to salt based or acid based solutions but I have not been able to find a supplier.

Help

William S [last name deleted for privacy by Editor]
- Glendale California


(2001)

Rhodium Plating Solution

A. Hello and hope you be well

Rhodium electroplating bath are:
a. Rh sulfate/H2SO4
b. Rh phosphate/H3PO4
c. Rh phosphate/H3PO4+H2SO4
d. Rh sulfamate
e. Rh fluborate
** f.molten cyanide**
g. Rhodium pentachloro amine/NH3

The best regards

Amirshahram M [last name deleted for privacy by Editor]
- Iran, Tehran


(2007)

Q. Well, I am doing rhodium, gold-silver plating works, so I am interested in this field. But I want to create something new, e.g., Different color shades in Rhodium (black, blues white, steel grey, blue, antique) In gold plating I want to create different color shades, e.g. pale yellow, pink gold, green yellow, antique gold etc. So please send me information or books, catalog or cd.

Thanking You.

Pradip S [last name deleted for privacy by Editor]
rhodium plater - Mumbai, Maharashtra, India


Gold Plating Technology

A. Hi Pradip. Coloring of gold is a well established artistry, but you can get some hints in the literature, including Goldie's book on gold plating. I have heard that there are some proprietary colors available in Rhodium plating, but I don't know of any publicly available info about it. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Rhodium sulfate solution vs Rhodium phosphate Solution for plating

September 13, 2016

Q. What is the difference between rhodium sulfate and rhodium phosphate solution when performing rhodium plating?

I was informed by a plating company that rhodium phosphate plating solution can only reach thicknesses between 0.01 µm to 0.025 µm. Whereas rhodium sulfate plating solution can reach from 0.5 µm all the way to 2.5 µm before it starts to crack.

Is this true?

Robert Lee
Jeweler - San Francisco, California, USA

6338
September 2016

A. Hi Robert. According to one vendor of rhodium plating solutions the thrust of that is largely true, although I think your decimal point probably belongs one place to the right for the rhodium phosphate...
Johnson Matthey says their RhPO4-based RJ100P is bright and lustrous to 0.5 µm with a recommended maximum thickness of 1 µm, whereas their Rh2(SO4)3-based RJ100S is bright and lustrous to 2.5 µm.

I might take issue with the wording "starts to crack" though, since I think most rhodium plating, including satisfactory plating, is cracked. You might find this study of the three major types of rhodium plating solutions interesting =>

Good luck.

Regards,

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


September 14, 2016

Q. Thank you Ted.

I have gone through the paper and am a bit confused by its findings. It lists 5 mixture options with intended thicknesses.

1.Rhodium sulfate + sulfuric acid is for >0.05 µm but seldom for >0.2 µm. (The experiment performed does show that 5 min of plating will reach 0.5 µm)

2.Rhodium sulfate + phosphoric acid is for thin decorative deposit. (thickness not mentioned)

3.Rhodium phosphate + sulfuric acid is similar to Rhodium sulfate + phosphoric acid (thickness not mentioned)

4.Rhodium phosphate + sulfuric acid is ideal for low deposit thickness such as 0.1 µm

5.Simple rhodium sulfate processes without additives of any sort can reach up to 2.5 µm - 5 µm

What is considered a simple rhodium sulfate process without additives and what is not?

Thank you again for the help

Robert Lee
Jeweler - San Francisco, California, USA


September 2016

A. Hi again. I am not a rhodium plating expert and cannot offer any deep thoughts that are not in that paper and other available papers.

However, in answer to your more general question, the plating industry tends to reserve the terms "addition agents" or "additives" to materials like grain refiners, brighteners, hardeners, and surfactants; these are mostly/usually organic compounds. Acids and salts (with the possible exception of sparingly-added salts of an alloying metal) are not considered additives. So all 5 of those bath descriptions, as they stand, are "without additives".

Regards,

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


September 19, 2016

A. Hello Robert, when I was in the field I had many customers that used our Rh sulfate based solutions. When a customer wasn't happy with the whiteness or brightness of the piece, we would advise them to add a small amount of phosphoric acid to the bath. If memory serves me correctly, it was around 10 ml/gal. The thickness of the deposit is not greatly affected. Check with your supplier and they can advise you on the correct amount to add based on your bath make up. Hope this helps.

Mark Baker
Process Engineer - Phoenix Arizona



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