posted 03-10-2008 11:49 AM            

This is obviously not something that should be done often because all cleaning, mechanical or chemical, involves removing some metal, and of course a concern for patina would probably preclude the use of chemicals altogether.

Apparently, many a piece of colonial and early American silver began it's life with a dilute sulphiric acid bath.

Hopefully, this suggestion has not already been made. Sulphiric does not come up in a search of all the forums.

posted 03-10-2008 06:45 PM            

When sterling is heated to annealing temperature it turns black. When pickled the sulfuric leaches out the copper on the surface and it goes a creamy white (that "dead" white) that is quite lovely but will not stand up to time or handling without waxing or such. Most of the silver in my shop being worked on is white and only when I give it the final polish does it come up silver. In fact most people seeing it do not realize it is silver.

Now days silversmiths use a buffered form of sulfuric which (do not ask me how, maybe Argentum 1...?) means I no longer have holes in my clothes!

P.S. It was always fun having the debate with the motley crew in the workshop of "Do you add the acid to the water or the water to the acid???" One gives a lovely warm reaction in the bucket, the other (which I have never seen) an awful chemical eruption.

posted 03-11-2008 11:08 AM            

One can also use that technique of surface depletion of copper from a silver alloy to produce the effect of a plated pure silver layer - the Incas, and I think the Romans, did that. They apparently used repeated applications of acid alternated with burnishing. There's a term for it, at least in the Incan context, but I can't seem to remember it.

posted 03-11-2008 12:44 PM            

Without getting into a lot of chemistry; sulfuric acid is partially neutralized to a point where there are a few protons instead of a lot of protons left and the pH range is still on the acidic side. The acid still reacts with the copper but not as quickly. It is similar to using strong vinegar. The smell is very strong but then diluting the vinegar and not smelling nearly as strong. Not exactly the best analogy. When adding acid to water a glass or inert rod is used to stream the acid into the water while moving the rod around a bit. This allows for a more uniform mixing to avoid building up heat. There is no explosion but rather a sudden production of steam which may seem to be explosive.

posted 03-11-2008 04:18 PM            

This is why repairs that involve soldering (silver solder, i.e. high temperature not lead solder or low temp.) change the color of old silver. The fire scale and pure layer have been disturbed, usually the fire scale covered up and a new layer of pure silver and the piece looks new. Or some variation on that because the piece might not have had fire in it because the smith stripped it out to begin with etc.

Not to go on and on but silver dips will do the same thing eventually that is turning your object white. Also most silver smiths keep their pickle hot, it's the first thing I do in the morning, light the torch and gas ring under the pickle pot. So the long and short is yes you could use sulfuric acid in solution to clean the tarnish off of silver but be prepared to rub it up afterward.

Lastly, I usually use regular silver polish unless there is a problem like it went through a fire or has corrosion spots, or is completely black. After many years it seems to be the best and in the end easiest!

And I would like to thank FWG for the mnemonic and Argentum 1 for the explanation, which does make it clear. No, we never did add water to the acid but with young students it was always a debate that needed the logic pointed out!

posted 03-12-2008 09:56 AM            

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Originally posted by argentum1:
h2so4 should stay in the realm of the chemistry department -

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"You'll never get it all back!" In my much younger days in the Navy, I used to crawl across the tops of 126 cell lead acid batteries with cells that weighed a ton each taking specific gravities, checking electrolyte levels, adding water, and even "spiking" cells when needed which of course meant constant contact with sulfuric acid. And that doesn't even scratch surface of all sulfuric acid that's out there in lead acid batteries that are everywhere.

posted 03-12-2008 11:07 AM            

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I have only seen a bowl made of lead used for this, and would query the use of copper.

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I was wondering about that too. It's been so long since I worked in the studio that I don't trust some of my memories, but we always kept separate pickles for silver and copper because copper would plate out onto silver if they used the same bath (that I did see happen). I was always told it was because the copper ions would go into the acid solution and you would get - at least under some circumstances - an electrolytic reaction. But on the other hand I remember using large copper tongs in the pickle - but maybe that was just the copper pickle, and I've forgotten the tongs for the silver.

posted 03-12-2008 11:17 PM            

If you have pickle in a copper bowl or use copper tongs (as I do) it would make no difference as long as any amount of iron (even tiny filings) never contaminated it. But if you had the pickle in a lead or glass bowl it could still happen because the acid solution is removing copper every time you pickle sterling and after a while if the binding wire was dropped in it would plate the silver with copper.

Thinking about the use of copper to "boil" silver pre 1900's it seems that it was the most commonly available metal that would not react with the silver. There was nothing else except lead but I imagine that the technology to heat a copper vessel (with charcoal) was easier than to heat a lead one.

By the way boiling is not what happens - I mean if I let the pickle boil it will either bubble out of the pot or boil off both being a pain and needing replacing of the acid and/or water. The proper temperature is below boiling where it is hot enough to do the job but not to evaporate to fast.

Bascall, thank you for that image of little you going across those huge batteries... not the normal idea of what a sailor might have done! I wonder if Silliman saw Noyes at work?

posted 03-13-2008 11:38 AM            

Thank you to all for your responses to this topic. They were very educational. The information about the pickling process producing what sounds like a silver plate on the surface of a piece was especially interesting.

posted 03-14-2008 10:14 AM            

I do wonder if any other metal has been tried as a substitute for copper in sterling.

posted 03-14-2008 12:10 PM            

quote:

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Originally posted by ahwt: I do wonder if any other metal has been tried as a substitute for copper in sterling.

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Argentium has a portion of germanium along with copper and 92.5% silver, and appears to diminish the effects of firescale and tarnish. Maybe someone else can comment further on this relatively new silver alloy.

posted 03-15-2008 08:32 AM            

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Most likely, there is also a Hezekiah Silliman connection here too, but I can't make it. Considering Hezekiah's mother's maiden name, Selleck, it seems posssible that Benjamin is Hezekiah's nephew.

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According to the Barbour collection, Gold Selleck Silliman is the son of Ebenezer and Abigail Silliman which would make him the brother of the silversmith Hezekiah Silliman and Benjamin the nephew of the same. Gold Selleck Silliman was born 7 May 1732 in Fairfield, CT.