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topic 37592

Bright dip for silver


(2005)

Q. I am looking for a non-cyanide formula to bright dip silver plated electroforming mandrels?

Mike McChesney Mike McChesney
Annandale, Minnesota



Nitric Acid Bright-Dip for Sterling Silver

September 18, 2017

Q. I need assistance in Brite Dipping of Sterling Silver. I use a heated Nitric Acid bath to remove oxides that form on the sterling silver from excessive heating... what I'm trying to remove is Cuprous Oxide which forms when the copper in the alloy oxidizes deep in the material. This is also one of the last steps in my operation before the finishing and polishing operations so I need the etch to very clean. The silver objects being manufactured are sterling silver trophies, cups , and platters.

I have a 150 liter bath that starts out at 30% concentrated Nitric Acid. I fill the tank with Nitric Acid that has already been diluted by the lab. The bath is heated to 130 degrees Fahrenheit once a day for approximately 2 hours. The silver objects are submerged in the bath for approximately 8 seconds. Every two days I top off the bath with approximately 5 liters of the same 30% concentrated Nitric Acid because the level in the bath drops due to evaporation... Currently we run the brite-dip bath for 2 months and than have a company come and pick up the waste and dispose of it. For the 2 months the bath is not monitored/titrated. At the end of the two months the bath is very blueish-green and the silver surfaces come out with excess drag lines or sometimes silver crystallization that looks like frost growing on the surface.

I have only tested for silver concentration and the results were 19,000 mg/L (ppm)

Some of my concerns are:

1.) When my brite-dip level goes down because of evaporation, what is evaporating is it water or Nitric Acid?

2.)Does the Nitric Acid get used up and the bath becomes weaker? I constantly top-off the bath with 30% concentrated Nitric Acid. I am under the assumption that the water is evaporating and because I keep adding Nitric the concentration of the bath increase.

3.) If sterling silver is the only thing going in this bath what is the by-product? I would guess Silver Nitrate, Copper Nitrate, and that nasty cloud of yellow smoke which gets sucked up by my ventilation.

4.) Ideally I would like to both reclaim my silver and remove the copper so I can continue to use my Nitric Acid indefinitely.

5.) Why at the end of the 'life' of the bath does silver crystallization deposit onto my piece and how do I prevent it?

Any direction would be greatly appreciated.

I am currently trying to use Pro-pHx Acid life extender as an option. However the blueish green color of the bath is still present so I assume it is not doing as much as I need. I think for a clean etch I need a very clean acid.

I am also ordering some lab equipment so I can titrate in house to see what my concentration is at the end of the 2 months. I would like to use bromoscerol green but haven't found any formulas to use it for titration.

Preston Jones
Silversmith - Providence, Rhode Island, USA


September 20, 2017

Q. I am looking for a Brite_Dip bath that gives the brightest possible finish to sterling silver...Currently I use a heated Nitric Acid bath to remove oxides that form on the sterling silver from excessive heating. What I'm trying to remove is Cuprous Oxide which forms when the copper in the alloy oxidizes deep in the material. This is also one of the last steps in my operation before the finishing and polishing operations so I need the etch to very clean. The silver objects being manufactured are sterling silver trophies, cups , and platters.

I have a 30% concentrated bath of Nitric Acid which is heated to 125 °F. Over time my bath turns blue and I have silver crystallization which looks like frost, I believe deposited onto my pieces.

-What are some additives that may be recommend for achieving a brighter surface in a Nitric Acid Brite-Dip solution for sterling silver?

-How can I remove the buildup of impurities in the solution?
Can I do this and continue to use the Acid Bath?


I am currently trying to use Pro-pHx Acid life extender as an option. However the blueish green color of the bath is still present so I assume it is not doing as much as I need.

Preston Jones [returning]
- Providence, Rhode Island, USA


September 20, 2017

A. I'm sure I'm missing something but it seems to me that you should avoid the oxide layer all together. I assume it is forming when your items are heated. Coating the item with a boric acid slurry or some commercial oxide inhibitor before heating should eliminate the need for this strong acid bath.

Neil Bell
Red Sky Plating

supporting advertiser
Albuquerque, New Mexico
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September 20, 2017

Q. Neil you are correct ... preventative measures are definitely taken. The type of flame (reducing), boric acid coating, and even gas flux in the torches. The problem is soooo many hearings and for little by periods of time, at least 3 or 4 annealings for metalspinning, and often 5 soldering operations for a silversmith, using hard solder (80%-65% silver in the solder). And even sometimes firescale (cuprous oxide in the castings).

The oxides are minimized but unavoidble. Depletion guilding also doesn't help because of the extremely high polish necessary on the silver. We are not the kind of shop to silverplate over our work either.

The main issue is how to precipitate out the copper and silver nitrate so I can than filter out the particles and continue to use the same acid.

Preston Jones [returning]
- Providence, Rhode Island, USA



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