Grayish White Powder in Nitric Solution

[juxtaposedsoul]

Hey, This is my first post and I guess I should give you some background before asking my question. I started buying/collecting gold and silver a few years back, mostly for investment purposes. About 6 months ago I randomly stumbled on some information that PM's can be refined at home, so I began investigating the methods/procedures/risks/rewards, etc. The more I learned I realized that refining PM's was right up my alley. I am a senior laboratory supervisor for an independent materials testing agency. I spent six weeks reading and re-reading CM Hoke's book. I scoured the web for all info on refining that I could find. Naturally, that brought me to this forum where I have been lurking for several months and reading every post on every topic. I sincerely appreciate this forum and all the advice and direction given by the various members.

I decided to start with silver. I may be wrong (I know I will be wrong many times) but I felt like I needed to "learn the ropes" with Ag. I intend to refine gold but only after I have become completely adept with silver. I have processed 11 batches thus far using homemade nitric. The first ten were precisely what I expected and yielded a very high quality finished product. I cast the silver into bars and rounds which I stamp and then keep. However, my last batch contained a fairly large quantity of a grayish or grayish white fine powder in the nitric solution after digesting about 50 grams of sterling jewelry. I use heat to accelerate digestion, let the solution cool and I dilute the remaining nitric with an equal amount of distilled water. I then filter the solution into another beaker for precipitation with a C110 copper rod (99.9% copper). Suddenly there is a grayish powder at the bottom of my digestion beaker, and even a few remnants of undissolved jewelry. This powder is like a cement and the bits of remaining jewelry are actually stuck in it! I rinse everything through the filter and capture this grayish powder. It does not effect my batch, and the yield is good. What is this powder? I rinsed the powder into a clean jar with distilled water and it settled in about 2 hours, leaving clear water.

Any help would be appreciated as I am still very new to refining and just trying to learn a little more everyday. Thank you to everyone.
Greg

 

[butcher]

Was the sterling silver clean, or was there soldering of joints? or epoxy?
Will this powder dissolve in boiling water? like lead.
How will it react with more nitric acid?
Could you have dissolved jewlery that was not just sterling?
I assume your copper was cleaned well.
sorry all I have is questions also.
But here on the forum you are sure to find answers.
fun thing about science we do not alway's know what we have.

 

[juxtaposedsoul]

Thanks Butcher,

Already I recognize my ignorance as I have not tried dissolving the powder in boiling water, nor in nitric. I will attempt both this evening and post the results. As for the metals there was one piece from which I removed a fairly large stone and several of the pieces may indeed have had solder. All in all I felt the metals were as clean as any I had previously processed. But perhaps not.

 

[juxtaposedsoul]

Update on grayish powder: First of all I may have been unclear in my original post- the powder was present immediately after dissolving the sterling and had nothing to do with the copper I used to precipitate the silver. It may be of note that I use nitric sparingly and the level of acid got very low in the hot beaker while digesting the sterling. As for the grayish powder dissolving in either boiling water or nitric- no, it did not. In boiling water I attained partial suspension of the solids while much of it just stayed at the bottom of the jar despite vigorous agitation. The nitric had no visible effect. Strange. While I really would like to know what this powder was I went ahead and disposed of it after running these two tests. The heavily diluted waste/acid/water/strange gray powder solution left a gray residue when being disposed. I had approximately 2 grams of this powder and 20ml nitric, to this I added 4 gallons of water. It may be of note that the water was gray.

 

[Barren Realms 007]

Update on grayish powder: First of all I may have been unclear in my original post- the powder was present immediately after dissolving the sterling and had nothing to do with the copper I used to precipitate the silver. It may be of note that I use nitric sparingly and the level of acid got very low in the hot beaker while digesting the sterling. As for the grayish powder dissolving in either boiling water or nitric- no, it did not. In boiling water I attained partial suspension of the solids while much of it just stayed at the bottom of the jar despite vigorous agitation. The nitric had no visible effect. Strange. While I really would like to know what this powder was I went ahead and disposed of it after running these two tests. The heavily diluted waste/acid/water/strange gray powder solution left a gray residue when being disposed. I had approximately 2 grams of this powder and 20ml nitric, to this I added 4 gallons of water. It may be of note that the water was gray.

Never discard anything till you know 100% what it is. What you had might have been silver chloride, it will not dissolve in nitric or water, but it will dissolve in ammonia.

 

[juxtaposedsoul]

Thanks for the reply. You are right, of course, about never discarding stuff. I am a little upset with myself for that since I really took Hoke's advice to heart and I save EVERYTHING for incineration and later refining. I should have tossed the filter with the gray powder into a Ziploc, inside a sealed jar, to deal with later once I learned what it was. The possibility you suggest of silver chloride is sort of what I suspected. Bummer. I may have tossed a couple grams of silver. This is why I chose to start with silver and work my way up. I would be really upset if I tossed a few grams of gold. I will take your advice to heart and always save, save, SAVE.

Because the majority constituent of the metals I dissolved was silver (and I test every piece prior to digestion) I thought it most likely that the strange gray powder was some form of silver. It certainly stains like silver chloride. I will almost certainly encounter this again and will check it with ammonia. Thank you for the help, it is greatly appreciated.

Greg

 

[Palladium]

It certainly stains like silver chloride. I will almost certainly encounter this again and will check it with ammonia. Thank you for the help, it is greatly appreciated.

Greg

Another test is to place it in direct sunlight and if it turns a purple tint. Then you know it's silver chloride.

 

[juxtaposedsoul]

Thanks again! My most recent batch on 7-4-11 also yielded some of this grayish powder. That is twice in a row after ten batches with just greenish-blue solution. This was a small batch just for experimentation and had only 30 grams of sterling in it. This time I saved the filter with the grayish powder that may or may not be silver chloride. Tomorrow I will expose it to sunlight and/or check it with ammonia. I am wondering if silver, during the process of dissolving in acid, becomes this grayish powder before it is fully dissolved into solution? I just figured that as molecules of silver separate from the main mass they go right into solution. Anyway, like I said I filtered the diluted solution into a beaker for cementation and retained the "dirty" filter. That is where things got a little funky. This time my filtered solution had a gray tint instead of the greenish-blue color I have become used to seeing. Obviously some of the very fine particles of the gray powder permeated the solution. I cemented at once with a new copper pipe to see what would happen with this "murky" solution. A light gray cottage cheese formed around the pipe, a little lighter in color and mass than what I usually see. This stuff did not precipitate because it never settled to the bottom, most of it floated. I filtered again and retained the "precipitate". The decanted solution was now the greenish-blue color I am used to seeing. I placed a copper pipe in it to see if I obtain further precipitate overnight. I dried the "floating cottage cheese" and it is very silvery in color with lots of tiny bright silver crystals. It actually looks very much like silver nitrate but I am highly suspicious of it because as a precipitate it did not have a specific gravity/mass great enough to cause it to drop. Question to the forum: should I just re-dissolve this and start over, or just add it to my silver nitrate container for future melting, or should I experiment with it and check it with sunlight/ammonia/boiling water, etc? Thanks in advance, and I know you guys are going to get tired of hearing this but I really, really appreciate the forum!

 

[kurt]

It could be tin paste &/or antimony from soft solder. Tin does not dissolve in nitric but turns to a white paste. Not sure of the effect of nitric on antimony but when you dissolve tin/antimony solder in HCL the tin dissolves leaving a black residue of antimony. So white tin paste & antimony residue from soft solder would leave a gray residue.

Try putting some “dilute” sulfuric on it. That will dissolve tin paste. It’s very slow at doing so & needs to be diluted.

Kurt

 

[juxtaposedsoul]

Thanks Kurt, and everyone else. I believe the grayish powder is in fact a combination of tin, antimony and possibly lead, as well. It is not silver chloride. It seems the random handful of sterling I selected a few days ago had some unfortunate constituents. There may have been one or more pieces that were not solid sterling but merely plated. My bad. I sometimes buy as much as 4 or 5 pounds and just scratch test instead of filing every single piece. Also, a few of the pieces had stones which I removed long ago, but I recall some of them were cemented or glued into the jewelry. Would boiling the sterling help or should I just forget about trying to refine any pieces that have had glue, cement or heavy soldering? I get that the cleaner the raw material to begin with the cleaner the nitric solution will be after digestion, but I guess I thought that the process would separate the silver from the junk.

On another note, one more question- is it bad to carry out the process if some of the metals have not completely dissolved? This has happened four or five times and I have simply caught the solid pieces in a filter or just left them in the digestion vessel when decanting/rinsing/filtering into the cementation jar. Just curious. Thanks for taking the time and making the effort to help this completely humbled person who is really just beginning to grasp the awesome complexity of the refining process. I did not expect it to be easy, and it isn't. I will keep working safely (ALWAYS my first priority) and try to learn a little more each day. With guidance from the group here on the forum, and with a lot more practice and experience, I may be able to help others someday, too.

 

[kurt]

Greg

It doesn’t sound like you got any silver plated items in you batch &/or if you did it was insignificant to the process. Another words you primarily had 925 (sterling) silver in your batch so the ratio of Ag to base metal was not a concern. --- Keep in mind that – that is what refining is all about. --- It’s about “parting” the more valued metal (the PM) from the less valued metal (base metal) that it may be alloyed with &/or plated on.

Sterling – which is often marked with the numbers 925 instead of the word sterling – is marked with 925 because it is 92.5 % Ag alloyed with 7.5 % Cu (copper) or 92.5 % Pm to 7.5 % base metal.

So the question is not – have I removed ALL of the base metal before I start the refining process --- because if you had – you would not need to refine it.

Rather – the question is --- have I reduced (or minimized the) the base metal to now make it worth the cost of the chems & time to refine (or part) the remaining base metals from the PMs (Precious Metals)

So to answer your question --- “should I just forget about trying to refine any pieces that have had glue, cement or heavy soldering? “

First – the solder --- & the glue, cement issues are two different issues. --- Lets start with the solder issue. Soft solders are primarily made up tin, lead, & antimony alloys & some many contain small insignificant amounts of silver (look up solder on the wikipedia web site) So they are base metals & when dealing with sterling silver jewelry – used only to attach a clasp to a chain or a post to an ear ring so they are a minimal base metal compared to the silver - so most definitely worth refining --- As you have already learned – when you put sterling jewelry with soft solder used in its making in the nitric – the tin & antimony settle to the bottom as a slug – so you just parted the tin & antimony from the silver. --- You just refined (at least in part) the silver

If there was lead in the solder, - it went into solution with the silver - & if you cement the silver out of solution with copper the lead will stay in solution – meaning the lead is parted out in the cementing process. --- If you recover your silver from solution using the silver chloride method it will bring the lead with it – but you can part the lead from the silver chloride with hot water.

Concerning the glue, cement issue, - it is most likely such a small amount that it will most likely part out in the chem. process – or when you melt your silver – the flux you use will flux it out. Or you could try using a solvent (like paint striper) to remove it.

Kurt

 

[Harold_V]

and just scratch test instead of filing every single piece.

That's clearly not a good idea, assuming you hope to avoid pieces made of base metals. I'm assuming your description is one of taking a streak from the item in question on a touch stone? Bound to yield poor results if that's the case. I highly recommend you file a deep notch with the corner of a file if you have doubts. Testing with Schwerter's solution should reveal the presence of base metals, assuming you're familiar with the various color reactions. If not, test known pieces to become familiar with their appearance.

You can also test with just dilute nitric. The presence of a copper or nickel base should yield an immediate blue/green reaction of the solution, plus you may even witness brown fumes. The surface patina on etched sterling tends towards a very light cream color. Given enough time, the solution will drift towards a light green color as well. The addition of a few grains of salt, or some HCl will yield the familiar silver chloride.

Also, a few of the pieces had stones which I removed long ago, but I recall some of them were cemented or glued into the jewelry.

It is my opinion that you likely now know the source of the material that wasn't silver, although it may have been silver plated. Glued stones is generally a sign of extremely poor quality in jewelry, likely not to be found in sterling, but certainly not impossible. Assuming one had an item made of nickel (often found, even marked sterling), it would not produce any of the problems you encountered, it simply wouldn't yield any values.

Would boiling the sterling help or should I just forget about trying to refine any pieces that have had glue, cement or heavy soldering?

Incineration is your friend. If you incinerate anything that isn't silver, it's likely to melt. If, by chance, you have silver items that have been glued my almost any means, incineration should clean them adequately that there would be no issues with processing. Best of all, oils and other body gunk, that is often a part of jewelry, is eliminated. That's never a bad idea.

I get that the cleaner the raw material to begin with the cleaner the nitric solution will be after digestion, but I guess I thought that the process would separate the silver from the junk.

Great deduction, one on which I just commented.

On another note, one more question- is it bad to carry out the process if some of the metals have not completely dissolved? This has happened four or five times and I have simply caught the solid pieces in a filter or just left them in the digestion vessel when decanting/rinsing/filtering into the cementation jar. Just curious. Thanks for taking the time and making the effort to help this completely humbled person who is really just beginning to grasp the awesome complexity of the refining process. I did not expect it to be easy, and it isn't. I will keep working safely (ALWAYS my first priority) and try to learn a little more each day. With guidance from the group here on the forum, and with a lot more practice and experience, I may be able to help others someday, too.

The only real negative is by not dissolving all of the solids, if, by chance, as you obviously found in your last two examples, you have not eliminated base metals, in particular those that might be plated, there's a very good chance that the remaining base metal will cement some of your silver. That's precisely what happened to you on your first go-round, at least by my understanding of your well presented description.

So then, if you must use dissolution as a means of separating objects of value from those of no value, ensure they are fully dissolved. Best policy, however, is to eliminate them, so you don't end up with objects that are troublesome once dissolved.

Do not be too concerned about traces of contaminants that may follow your silver in cementation. I'm not suggesting that they are a good thing, but you have two additional shots at their removal. One of them is when you melt the recovered cement silver. Do that by fluxing ONLY with borax, and do not add the borax mixed with the silver. That's a recipe for suspended prills that can be difficult to recover. Instead, assuming you are melting in a furnace, or a melting dish, start melting the metal without flux. When the surface becomes fluid, sprinkle on a small amount of borax (anhydrous or borax glass is highly recommended for this process. It melts in a very tranquil manner). That will help the molten metal flow and agglomerate, capturing the oxides of contaminants in the process. The final refining in a silver cell will remove the balance of impurities, primarily copper.

Harold

edit: corrected a statement, which has a profound effect on meaning.

 

[juxtaposedsoul]

Kurt and Harold,

Thank you! I have learned more from these two posts today than I have learned on any single previous day. Excellent advice. Many, many thanks. I will now incorporate incineration as the second step in refining silver, with the first step being a conclusive determination that the item(s) to be refined is in fact substantially silver. I am familiar with basic testing procedures and while I always take appropriate steps to insure I have purchased/obtained gold of the specified purity, I have allowed myself to become lax with sterling. In other words if it is clearly stamped 925, 950, STER, Sterling or TAXCO- and it scratches true with a red color (light green with no fizzle for lesser silver alloys) when nitric/muriatic testing acid is applied- then I have just assumed it was sterling. I am now finding that some of the pieces I have are not sterling.

I have been very, very pleased with the first ten batches I refined. The largest was only 150 grams, and most at 100, but they yielded a beautiful blue solution that dropped perfect silver cement. The melts went well, too, although I find despite having a lot of experience with metalworking (heating, torch-cutting, welding, brazing, etc.) silver is an entirely different animal and difficult to get nice looking rounds or bars. The Ag seems to solidify too darn fast when I am pouring, but I am getting the hang of it. I learned that positioning is everything when trying to pour molten silver, because if your melting dish and mold are too low or too high you do not have adequate control over the pour. Tricky stuff. I would like to post a pic or two of what I have done so far, but while it looks good to me many of you will undoubtedly get a good chuckle. My bars do not look exactly like Englehard's.

Again, thanks a billion for the replies and guidance. I will now re-read what you have posted again, several times, to make sure I fully comprehend your words. Then- my ritualistic evening reading of Hoke. I honestly shudder to contemplate what would befall a novice refiner like myself without her words of wisdom.

 

[Harold_V]

I would add----when I refined, a small percentage of items marked as sterling were made of German silver, which, as you know, contains no silver. They were typically made in Mexico. Be suspicious of items that have a slight yellow appearance. Once you have identified such a piece, you'll be able to discern the difference between such items and sterling by visual inspection.

Harold

 

[qst42know]

Many items made of nickel alloy are marked only with the word

TAXCO

, don't include them unless you have tested them to be silver.

A word of warning! Several famous silversmiths worked in Taxco Mexico. Search "Spratling", "Margot" and several others on eBay or the open web and you will find many items worth hundreds of times the silver content. Either way don't digest it until you have identified it!!!

Hundreds of times may be a slight an exaggeration (adjusted for $36 spot silver) unless it's an early piece made by their own hand.

 

[juxtaposedsoul]

qst42know,

Thank you. While I am aware of Spratling and many of his different hallmarks, I never thought to consider his works may be more valuable than the actual silver in them. Great point. Sadly, I have in fact destroyed two of his pieces circa late 40's. Bummer. I will do more research on him and Margot and other renowned silversmiths to learn how to properly identify their work. The Spratling pieces I still have will be separated from my other sterling and put in with my bullion for safekeeping. Thanks again for the excellent advice. For what it is worth, the two Spratlings I stupidly digested were very good quality, marked 950 with his stylized initials, and made one hell of a fine button! The Spratling Button was later re-melted with some silver powder and is now part of a one troy ounce silver round I cast last week. :lol:

And yes, you are right on about TAXCO-stamped jewelry. If it is not fully hallmarked with the eagle, the 2-letter code, and the numerical code of the maker it is often not real silver. Also, many items simply stamped 925 are not actually 925 at all.