Topic: Chemical Etch on Sterling Silver from Soap

We use animal fat based compounds to polish our parts. When we clean our polished sterling silver jewelry components in our ultrasonic cleaning systems we get a type of chemical etching / haze on the surface of the parts. This forces us to have to re-polish (dry wheel) the parts to remove this superficial phenomenon. Attached are pictures of this condition at 50 and 200X.

As you can see the copper portion of the sterling silver becomes separated / highlighted from the silver. Our sterling silver is 92.5% silver and 7.5% copper.

Through several DOE’s and test trials we have isolated the root cause to be the ultrasonic soap we use which is Oakite BCR Plus (6% mix). We are able to recreate this condition by just placing parts in the mixed soap over time w/o heat or ultrasonic.

We have done some preliminary trials with alternative soaps with some success. In particular we have had good results with Oakite Buff Brite NR (2% mix).

Can anyone suggest a soap that would work in this situation or recommend a soap supplier that may be able to help us with solving this issue?

Your help in this matter would be greatly appreciated.

   Pictures of the Condition.jpg

Last edited by SteveO@Tiffany&Co (06/22/2009 - 06:27 PM)


Re: Chemical Etch on Sterling Silver from Soap


I work for a chemical company out of NC. We have several products that I think may do the trick. With precious metals, sometimes it's a trial and error sort of thing.

Give us a call if you would like. (910) 892-1791

Hope to hear from you.

EnviroServe Chemicals, Inc.

(910) 892-1791


Re: Chemical Etch on Sterling Silver from Soap

Afternoon Steve,

Paul Fisher pointed out that your question about animal fat compounds hadn't been answered.

Perhaps I can help. I am supposed to be a professional cleaning consultant..... :)

I wonder if your cleaning operations are leaving scrap animal compounds on the surface as a residue? Others in the jewelry business find that they leave microcrystalline waxes on surfaces after they clean them in aqueous cleaning baths using ultrasonics.

In order to clean these chemicals with ultrasonics, one normally needs to melt or soften them. I don't know what compounds you are using, but common melting points for these chemicals are at least 160 oF which is a fairly hot temperature for an ultrasonic cleaning bath.

Do you think this could be the source of your problem? Do you know the melting points of your animal compounds (probably C18 alcohols)? At what temperature do you run your ultrasonic bath?

Please respond as you think I can help

John Durkee


Re: Chemical Etch on Sterling Silver from Soap

Hello John,

Thank you for your response / help on this matter. Our ultrasonic wash tanks are at 140F. I am not sure what the melting point of our polishing / buffing compound is. There is no evidence of residuals on the surface of the sterling silver after cleaning.

The condition is more of a reaction to the soap by the sterling silver alloy when it is in a copper rich phase. The copper sections of the metal become chemically etched by the caustic soaps used to wash the components.

We are presently looking into terpene based solvents that are aqueous or semi-aqueous in nature. At the moment we are having good results using Petroferm's Bioact 280. The down side of this product is that it must be used at full concentration which makes it expensive to use.

Steve O.


Re: Chemical Etch on Sterling Silver from Soap

Hello Steve,

I have faced similar issues of surface etch and haze with a couple of my customers. Once was in cleaning polished sterling silver parts, the other mirror finished zirconium parts. Both processes used ultrasonic cleaning.

So, I thought I'd share my experience with you in the hope that it will help you with your current challenge.

- The sterling silver problem situation:

The cleaning process consisted of one ultrasonic cleaning tank, and one heated (static) rinse tank. The problem was high rate of rejects and reworks due to damaged surface finish after cleaning.

Attempts to correct the situation by changing chemical brands, strength, concentration, heat and cycle time were all to no avail, In fact, the high concentration, harsh chemistry, combined with the  amplifying effects of long ultrasonic cycle time did nothing but accelerate and increase the surface etching. On the other hand, the haze remained as it was in the domain of carry-over from from the buffing compound residues.

- Here's how the issues were resolved:

Step 1: Pre-clean at 175-180ºF (higher if no ultrasonic used) with a brief ultrasonic coupled with oscillation (up+down movement). While the proper parts positionning, chemistriy and heat are instrumental to dissolve the fatty compound, oscillation proved helpful to "release" the contaminant off the surface. Also, this step helps prevent air entrapment as the parts in question have fine details like brazed appendices, tiny holes and knurled areas.

This tank is equipped with adequate filtration and recirculation system to handle both of types of contaminants present in suspension and in dissolution, and hence reduce the carry-over to a minimum into the precision cleaning step.

Step 2: Ultrasonic cleaning using specialized ultrasonic cleaner at 140ºF. Specialized ultrasonic detergents are more expensive than general purpose's, but proved less expensive to use. They are more reliable in getting a faster and repeatable sequence of cleaning operations (but this is beside the point for now)

Step 3: A heated, cascaded/counterflow city water rinse.

Step 4: DI water rinse

Step 5: Hot air drying

NOTE: In the zirconium experience, step 3 is skipped as the parts have plain smooth surface.

Hope this helps. I'll be happy to answer any questions you may have regarding this information

Clement Gemayel


Re: Chemical Etch on Sterling Silver from Soap

Also, check out our article by Barbara Kanegsberg and Ed Kanegsberg on Troubleshooting Your Ultrasonic Cleaning Process for more information:

Metal Finishing Magazine

Jason Awerdick
Marketing Manager, Metal Finishing
360 Park Avenue South, New York, NY 10010-1710
Phone: 212.633.3103 | Fax: 212.633.3140 | E-mail: |


Re: Chemical Etch on Sterling Silver from Soap

Well, after two years of investigative work on this matter I have found three different solutions to the issue. They are as follows:

I. Mechanical Solution by Cool Clean

This is a waterless system that uses a terpene solvent with ultrasonics and a CO2 rinse. It is quite expensive but it eliminates all the limitations, expenses and the waste treatment of of using water. The solvent and the CO2 are distilled and reused. The parts have never been any cleaner!

II. Chemical Solution

a) Deconex 38CU by Borer

This is an additive that can be added to our current 2% soap solution that inhibits the corrosion of the copper in the sterling silver alloy. The added quantitiy by volume is 0.3%. It is a little expensive and has long lead times for getting the additive here from Europe. It also has a sweet odor that can be noticed in the wash area but there is no more "copper haze" seen.

b) Oakite Inhibitor CB by Chemetal

This is very similar to the Deconex 38CU (0.3% added to wash solution) but it is less expensive, easier to obtain locally and has less of an odor.