# Gold Nugget not dissolving



## Noxx (Mar 25, 2007)

Hello,
I've puted two gold nuggets in Aqua Regia. One dissolved completly but the other one turned black and did not dissolved... Why ? Is it because there is silver preventing it to dissolve ?
Thanks


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## lazersteve (Mar 25, 2007)

Noxx,

It's some sort of impurity, could be flux, higher PGMs, or silver chloride. Silver chloride is usually white though. Does heating the solution cause it to dissolve?

Steve


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## AgAuPtRh (Mar 25, 2007)

If you have the ability noxx---it's best to roll your nugget out or flatten it. 

Heat it up a tad and roll it or pound it flat. Twist it so it doesn't lay flat in the dish. The more surface area for the acid to work the better. 

You may not have had enough AR to complete both nuggetts too. 

I've had the same happen with electrical contacts. So I just digest one contact at a time. 

Hope that helps.

AgAuPtRh


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## Noxx (Mar 25, 2007)

Thanks for the replies. My AR were on an hotplate at 40-50°C. I will flaten it.
Thank You


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## Noxx (Mar 25, 2007)

OK, I just took my nugget from the acid mixture... My nugget isn't black. It is has a deep purple layer (easily removable). What is it ?
Thanks


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## lazersteve (Mar 25, 2007)

Purple is usually colloidal gold.


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## Noxx (Mar 25, 2007)

Well, it's not... It a kind of wax. As soon as I puted the flame on the purple powder, it melted instantly into a ball. When cold, this bullet is hard rock lol.
I don't know what it is...


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## AgAuPtRh (Mar 25, 2007)

The action of hydrochloric acid on silver--even in aqua regia will turn the silver a gray color developing a whitish layer of silver chloride. It can turn purple in sun light.--a lavender color then turn to black.

After heating your nuggets in aqua regia---what color did the solution turn to?

Karat gold---gold alloy with copper will turn green.


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## Noxx (Mar 25, 2007)

It was mostly pure gold nuggets +95%. My solution took a yellow color. But it was outside so sunlight may had an effect.
Thanks


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## Harold_V (Mar 26, 2007)

> Heat it up a tad and roll it or pound it flat.



It is likely hot short, thus won't respond to heating---it will simply crumble if so. Pounding on it would result in lost alloy. Gold is not known for being worked hot with success. It should be rolled cold----or melted and poured in water to create "corn flakes". They break down readily, assuming silver content isn't too high. If they are, the button should be inquarted, pelletized (corn flakes), then base metals removed with nitric acid before attempting to dissolve the gold with AR. It's never a good idea to attempt to process buttons of metal. It takes too long. 



> You may not have had enough AR to complete both nuggetts too.



Highly unlikely. Both would have been dissolved somewhat equally were they of equal composition. The problem is likely a presence of too much silver, or an insoluble element, though how that would have been combined with gold I have no clue. 

If the button had a green cast before beginning the operation, most assuredly the gold contains too much silver. While silver chloride is white, it isn't when it doesn't form freely, such as when precipitated from a nitrate solution. When one attempts to dissolve gold in heated aqua regia that contains too much silver, it will eventually have a dull, green cast, and will resist dissolving indefinitely. You can boil it for days on end with no results. The presence of silver, reacting with chlorine, creates an impervious shell of silver chloride which isolates the gold from the acid. It is that shell that appears to be a dusty green color. 

Harold


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## AgAuPtRh (Mar 26, 2007)

Yup noxx----even reagent grade acids can be limited in how they work. Giving the acid as much surface area as possible by rolling and flattening can increase the acids ability to work and also help the acid to work faster. 

The build up--waxy stuff as you put it--if it turned color after coming out of the acid--was probably silver and probably the reason your nugget stopped digesting. 

Sun light shouldn't have an effect until your chlorides are out of the acid and shouldn't effect the color of the acid at all. 

Digesting all of the base metals first----before refining your gold will help you refine a purer product. So---if you do a hydrochloric acid first--wash--then do a nitric acid---wash---then you are left with as much gold as possible before treating with aqua regia. By removing the base metals first you also have less garbage for the acid to work on and less garbage in the solution from which you will be dropping your gold. 

Roll and flatten
Treat with hot hydrochloric
Treat with hot nitric
Wash between treatments
Finish with Aqua regia

A purer gold will result.

Patience is the key


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## Harold_V (Mar 26, 2007)

AgAuPtRh said:


> Roll and flatten
> Treat with hot hydrochloric
> Treat with hot nitric
> Wash between treatments
> Finish with Aqua regia



Sigh!

Your sequence is wrong. Once you introduce HCL, you can't introduce nitric, and if you introduce HCL first, you won't remove silver. 

Nitric should be the first reaction, removing all base metals. If the gold is properly inquarted, there will be very little base metal and silver left in the now honeycombed gold, and won't present a problem. Washing the lot one time with tap water is adequate, then AR should be introduced. What little silver is left behind will readily convert to silver chloride and be recovered when the gold chloride solution is filtered. 

As an added note, nothing to do with this particular post------there is absolutely no need to use distilled water in any of these processes. A small amount of silver will convert to silver chloride, but that is not lost. Trace elements in tap water, aside from chlorine, present no problems for the refiner. There is no need to spend money for distilled water unless one is working with silver nitrate intended for use as an electrolyte, or making test or standard solutions. 

Harold


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## Noxx (Mar 26, 2007)

Thanks for all the great info. I'm currently building a tutorial on the subject.
But note that my nuggets are +95% purity before I added them to the AR. Maybe the one who did not dissolved had a surface layer I don't know...
I will try to «corn flake» it lol :lol:


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## Harold_V (Mar 26, 2007)

Noxx said:


> Thanks for all the great info.



You're welcome!



> I'm currently building a tutorial on the subject.



That's nice------but it would serve the readers very best if it was good and proper information. There are tried and proven methods for standard refining that are easily accomplished----with no real reason for anyone to "re-invent" the wheel. There's a fair amount of misinformation being tossed around that is sure to create problems for some of these guys, or complicate what should be an easy process. Working with silver chloride is one in particular. 

I'd suggest you do your research well, and choose a procedure that is in keeping with good practice. Lots of wives tales need to be abandoned so these guys can move forward with proper learning. 



> But note that my nuggets are +95% purity before I added them to the AR.



I'm curious how you know that. Properly refined gold should exceed 95% first time through, and have almost no silver. Rose suggests that a few atoms of silver will behave as gold and be difficult to eliminate, so a trace, at best, should show in once refined gold. Other base metals may differ, but they wouldn't prevent the dissolution of gold in AR. 

After posting my comments, I read further and agree, the purple film you found was likely silver chloride, but it had obviously photo-reacted with sunlight. It's also possible for the gold chloride, absorbed by the silver chloride, to have done the same thing. Gold chloride, exposed to light, will leave purple stains on almost anything it touches Everything you described typifies what you would have experienced had it been silver chloride. The green coloration I spoke of would have been only if you had been working out of sunlight, and had not photo-reacted. 

I assumed you were working indoors, in a fume hood, ---but realize most of these guys don't have that luxury. 



> Maybe the one who did not dissolved had a surface layer I don't know...



I have serious reservations about a "surface layer", aside from one forming from residues that accumulate (like silver chloride). 



> I will try to «corn flake» it lol :lol:



They work great. By the time the insoluble layer has formed, the entire lot is usually dissolved, so the silver chloride just crumbles and turns white----and all the gold goes into solution. You may wish to look for some tiny bits that don't fully dissolve, for occasionally one of the flakes will have a heavy cross section. This process works very best if you use it for the preliminary operation, where you remove base metals via the inquartation/nitric process. 

The process of making the corn flakes is simple. Have a deep container (metal----never plastic), at least the size of a 5 gallon bucket. A grease can, one you might see in a place like Jiffy-Lube (about 20 gallons in size) would work great, but should be well cleaned if used). Fill the container with cold water, then melt your button with a torch. Pour the molten metal into the water filled container in a thin stream, moving around the container so you don't get an accumulation of hot metal in one place. It can fuse to the container if you don't have enough depth, or poor too much in one place at one time. 

You don't get shot when you perform this operation, you get, instead, flakes, best described as corn flakes, thus the name I applied. 

If you need to talk about the inquartation process, ask. It's fairly critical, in order to get the base metals out without breaking down the gold into fine powder. Hoke's book covers it perfectly, which is one of the reasons I keep telling you guys to buy the book. It also teaches you how to test metals. 

Harold


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## lazersteve (Mar 26, 2007)

Harold, 

I'm very interested in learning this process properly. I've come to realize, since meeting you, that there are much easier ways to do these things and you seem to have a very good grasp on what the CORRECT processes are. Please share your valuable knowledge with us.

I've begun accumulating some sterling silver items which I'll soon purify to elemental silver for use in these processes.

Thank you again,

Steve


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## Noxx (Mar 26, 2007)

Thanks for this very valuable info. 
I'm currently learning how to inquartate properly. But I'm looking for a good place to get cheap silver  I don't have any at hand, I only have jewelry that is +14kt so Nitric Acid can't dissolve it...
Thank You


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## AgAuPtRh (Mar 26, 2007)

After going back and reading a bit--I see where I messed up in the process. The hydrochloric wouldn't help. That was from another testing process. 

But I did find the next two paragraphs in C M Hoke's, Refining Precious Metal Wastes. It deals with "button" of melted Gold.

" If you have melted your filings into a button, the next step is to get the button in such a form that the acid can act readily. Sometimes it is so soft that you can roll it easily. Cut the rolled strips up short and twist them so that they will not lie flat in the acids. Roll them very thin; a few minutes at the rolls will save hours in later steps. Anneal.
Usually it is easier to granulate the button than to roll it. Remelt the button in a clean crucible with a little flux, and pour it while molten into a big bucket or tub of water. Pour it in a thin stream and the molten metal will break up into fine shots or pellets when it hits the water. Collect these pellets carefully."

Refining Precious Metal Wastes-C M Hoke 1940--pages 39 and 40.

This goes on to discuss the 'Nitric process" not hydrochloric. 

Thanks Harold. I'm glad you are here and appreciate the professional experience you bring to the forum. I hope you stay around for a long time.


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## Noxx (Mar 26, 2007)

I tried to put it again in new Aqua Regia and it's still turning black ! My solution took a yellow color but the reaction seem to slow down. I already remelted the nugget and pouring it in water.
Here is what my nugget looks like after pouring it in water.


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## Anonymous (Mar 26, 2007)

Harold_V said:


> Washing the lot one time with tap water is adequate- as an added note------there is absolutely no need to use distilled water in any of these processes. A small amount of silver will convert to silver chloride, but that is not lost. Trace elements in tap water, aside from chlorine, present no problems for the refiner. There is no need to spend money for distilled water unless one is working with silver nitrate intended for use as an electrolyte, or making test or standard solutions.
> 
> Harold



Harold, once again you surprise me. 

Please indicate what scientific basis you are relying upon to support your statement which apparently exempts ANY chlorine present in tap water used by these forum members? Yes, chlorine as you note is most assuredly currently available in tapwater. I would add those amounts vary depending upon ones distance from the substation where Clorine is routinely added by municipal water department personnel. 

Chlorine is one of the most potent of the 5 gold dissolving halogens. This is true when forum members are using sodium nitrate as well.

Can forum members assume you have some scientifically based quantitative measurement as to how much gold loss is acceptable, due to chlorine in tap water? 

It appears all forum members agree water is the preferred diluting solution for their urea nitrate muriatic based solution. 

Were you trying to say that because AR was about to be employed as the next step, that tap water wouldn't be any problem at this juncture with the exception of the chlorine in tap water?

How much gold loss is not acceptable to you? Or, should gold loss due to the exception you made for chlorine in your above quote be acceptable to others? 

It looks to me like these forum participants are scrapping and scraping for every brown powdered particle they can possibly corral or capture in their filters. 

Cost calculations versus results do not seem to be on high on their list of concerns.

a man named Sue


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## Anonymous (Mar 26, 2007)

Noxx said:


> Thanks for this very valuable info.
> I'm currently learning how to inquartate properly. But I'm looking for a good place to get cheap silver  I don't have any at hand.



Have you investigated any metals besides silver for your inquart process?
Silver is not your only option, fortunately. 

Since you are obviously into experimenting and reporting visually on outcomes, perhaps you would consider a series of videos showing various silver substitutes and how they perform in your process. 

It should be an absolutely fascinating series. May we look forward to seeing some results of your experimental based research on this substitute for silver series in the near future?

a man named Sue.


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## lazersteve (Mar 26, 2007)

Very interesting stuff Sue. Here's a quick patent search that supports your point:

http://patft.uspto.gov/netacgi/nph-...50&s1=4857107.PN.&OS=PN/4857107&RS=PN/4857107

This topic seems to have more to it than first meets the eye.

This patent even does a purity comparison to AR process and gives metal recovery methods for the PGM's.

Awesome results are coming from this discussion. Great question Noxx! I love to learn!

Steve


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## Noxx (Mar 26, 2007)

It's stange... I just took off the black nugget, get rid of the purple layer, remelted and puted it back in the acid. Only after 30 seconds, the nugget was all black again ! I have absolutly no idea whats going wrong. The gold IS dissolving but at a very slow speed...


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## Noxx (Mar 26, 2007)

I'm pretty sure my nugget is lightly alloyed with silver... When I melt the «wax», it turns white and small white nuggets forms...


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## Harold_V (Mar 27, 2007)

Sue said:


> Please indicate what scientific basis you are relying upon to support your statement which apparently exempts ANY chlorine present in tap water used by these forum members?



Simple!

Any dissolved gold will be precipitated by base metals. There is no loss, and there is no need for distilled water in this instance. 

For your information, gold comes off in solution and is converted back to a metallic substance when it leaves the proximity of the anode. These stripping cells are not something new-----the process was developed and patented long ago, to salvage expensive defense components with improper plating. How it works is no mystery, at least to me. Fact is, I've witnessed one of these cells in operation at a government installation in New Mexico. At that time ('75) they were stripping tens of thousands of troy ounces annually. 

Aside from your apparent understanding of chemistry, I question the amount of knowledge you have as a refiner. I come to you with more than 20 years of practical experience, with thousands of ounces refined, along with silver, platinum and palladium. Much of what you've had to say thus far doesn't square with commonly accepted practices that were the norm. Could it be you're trying to re-invent a round wheel? 

I'm still waiting for your explanation of how amalgamation works. Just claiming the accepted scientific explanation of old is not enough. Please provide cites. 

I do not consider losses of any kind to be acceptable, including financial losses that need not be incurred. 

Harold


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## Harold_V (Mar 27, 2007)

lazersteve said:


> Harold,
> I'm very interested in learning this process properly. I've come to realize, since meeting you, that there are much easier ways to do these things and you seem to have a very good grasp on what the CORRECT processes are. Please share your valuable knowledge with us.



Steve,
Aside from having applied the considerable knowledge I absorbed from Hoke's book, I claim no specific knowledge. I am not an educated person, and have no chemical training. What I am is good at following excellent instructions, and learning from those that went before me. For me to detail all the operations one would encounter would be akin to my writing a book in keeping with one already available----Hoke's. I'd look the fool to pretend to upstage him, if for no other reason, a lack of credentials. I would seriously encourage you to get a copy of that book----regardless of cost. When you compare the value against the cost, it's literally free. It will teach you proper refining processes and testing that may otherwise escape you. 

Please understand that I'm not against sharing what I know----and will answer questions as time permits, but I can't provide step by step instructions when they are readily available, backed up with good and proper credentials (Hoke's!)



> I've begun accumulating some sterling silver items which I'll soon purify to elemental silver for use in these processes.



Wrong move!

Do NOT purify them. 

Here's what you do: 

When you inquart, add your sterling or coin silver. Add it such that the end result yields an alloy comprised of 25% gold, the balance silver, copper, nickel and what ever else may be present. The whole idea here is to allow gold to be separated from silver, which can't be accomplished in AR as long as silver content is excessive. I hope that makes sense. 

The other thing to consider is that you have sterling or coin silver that needs to be processed to pure. You would do that by dissolving in nitric, and recovering with copper. 

Why do it twice? 

If you'll use scrap silver alloys for your inquartation, you get the benefit of running it free of charge in a sense, because you must add something to your gold, anyway. Better yet, and Hoke discusses it in his book as I recall, silver requires considerably less nitric to dissolve than does an equal amount of copper or brass. It's cheaper and faster to use silver, plus you get through the dissolving phase while parting gold instead of adding a second, unneeded operation. 

Please, if anything here is confusing, ask for clarification. 

Harold


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## lazersteve (Mar 27, 2007)

Harold,

You are a valuable asset to this forum. Regardless of your level of formal education you have the hands on experience. You know what works and that counts for a lot.

I'm going to purchase a copy of Hokes book tonight.

On the subject of the sterling you mention some of the other base metals. Are these other metals recommended or just okay to use if they are laying around? 

I have the silver and it's no problem to go with straight sterling (silver and copper alloy typically). I noticed while I was making the tutorial on separating gold from silver how easily nitric chews thru silver, much easier than copper or brass.

Should I cornflake the gold/silver alloy before using the acid on it?

You mentioned using AR in the inquarting process, everywhere else I've read mentions dilute nitric, which is the most efficient?

Lastly, is a second dissolution of the gold an absolute requirement?

Thank you,

Steve


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## Harold_V (Mar 27, 2007)

Noxx said:


> I tried to put it again in new Aqua Regia and it's still turning black ! My solution took a yellow color but the reaction seem to slow down. I already remelted the nugget and pouring it in water.
> Here is what my nugget looks like after pouring it in water.



I'm afraid I'm going to say, one more time, that you MUST get a copy of Hoke's book! You clearly don't understand the things you're experiencing, and need clarification. 

Please understand that I'm not trying to be rude, even if it appears I am. It's just that there is considerable information you must have in your head before you can make judgments about the things you're experiencing, and Hoke addresses them exceedingly well. Far better than I'm able, for sure. 

OK-----did you read my comments about the color of your button? Do you recall me telling you that if it was green in color, that it would contain too much silver to dissolve in AR? The picture you posted is terribly green, although I understand that it can be the result of the electronic photo, and in life is not really that green. If it is, you have way too much silver in your gold. That's a prime reason to not trust the cupel method for purifying gold-----it doesn't remove silver or the platinum group. 

White gold WILL dissolve in AR, for nickel will readily go into solution----so white gold could be processed directly by the AR process, although, to put it bluntly, it's a stupid way to go, and for various reasons. 

One of the reasons is that when you precipitate gold from dirty solutions, you drag down, mechanically, some of the contaminants that are in solution. From that you can deduct that the cleaner the gold is when you dissolve in in AR, the cleaner the metal should be that you recover upon precipitation. I treated all alloyed gold in the same manner as a result, including dental golds. By doing so, you got the platinum group mainly away from the gold chloride solution----adding it to your silver. That includes platinum, which, in spite of everything you feel you understand about it's inability to dissolve in nitric, it's not true when silver is present. In that circumstance, it *will* dissolve to a degree in nitric. (Hoke discusses that, too!).

In order to cut posting short, for I have limited time, the picture of your button which shows silver colored bits, that you called white gold. Sorry-----there's no reason for white gold to be present. What you're seeing is minute droplets of silver, reduced by torch from the silver chloride covering. If you can separate one from the main nugget, dissolve it with a drop of nitric and then add some table salt. You should get silver chloride. You also will likely see traces of gold, perhaps even colloidal. Gold chloride will have collected in the silver chloride and have been reduced by torch to elemental gold. 

Remember this for future use:

White gold is typically an alloy of nickel and gold, although on rare occasion you may encounter white gold made of palladium and gold. It is rather unusual because of the expense of palladium as compared to the cost of nickel.

Silver, combined with gold, is *not* white-----it's green. Like the picture of your button.

Harold


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## Noxx (Mar 27, 2007)

Thanks for this valuable info.
More the time pass, more I understand I must buy Hookes book ! What's the title again ? I'm must find a good source that ships to Canada at a fair price.
BTW, my nugget was not green. Currently, it is whiter than pure gold.
Thank you


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## Noxx (Mar 27, 2007)

-------->Refining Precious Metal Wastes C. M. Hoke. <---------
Everyone should get it


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## lazersteve (Mar 27, 2007)

I just got it on Amazon.com $120 and some change shipped to Florida.

Thanks Harold!


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## Harold_V (Mar 27, 2007)

lazersteve said:


> Harold,
> 
> You are a valuable asset to this forum. Regardless of your level of formal education you have the hands on experience. You know what works and that counts for a lot.



You can save yourself a lot of trouble if you'll trust me on these operations. I have no axe to grind, just trying to help people learn ways of refining that are tried and proven through years of use, almost in all cases by those that went before me. I made my share of stupid mistakes when learning, so if I can pass along some things to avoid, I'd certainly be remiss if I failed to do so. 

If I say something and don't offer an explanation for why I make a particular suggestion, I certainly am open to questions. I don't mean to leave out pertinent information, but this discussion can drag out until it literally fills volumes of books. There's so much to know in order to refine properly that it simply can't be covered in a few sentences. 



> I'm going to purchase a copy of Hokes book tonight.



I fully expect that when you receive it and start to digest the incredibly good information contained within, that you will quickly come to realize why I promote the book so heavily. Aside from particular information I own about advanced PM group refining, and some of the silver processes I used, everything I know came from Hoke's book, along with guidelines pertaining to gold extraction from ores from Rose's book. It won't take you long to come to terms with how little you understand about precious metal refining, and how valuable Hoke's book will be to you. I still have my copy----and wouldn't dream of parting with it. In truth, it represents what I have become-----including my early retirement. 



> On the subject of the sterling you mention some of the other base metals. Are these other metals recommended or just okay to use if they are laying around?



I avoided using anything but known silver. Brass should be avoided at all costs. It often contains tin, which makes filtration difficult in succeeding operations. When you find you have a solution that refuses to filter, it generally contains tin. There are ways to avoid the problem, which I'll discuss when appropriate. 

There's nothing wrong with using your silver over and over again aside from the fact that as you do so, if you deal with dental golds, or jeweler's wastes, it will gradually accumulate a lot of the platinum group metals. You can usually tell when they're present, for they come down last, after the silver, and always darken the silver. Once the silver has been precipitated, testing the solution with stannous chloride will tell you if you have values present, or not. The solution is generally green in color if so, not blue as you might expect. The solution will turn blue when the PM group has been precipitated. A little experience in that regard will be most revealing for you. Bottom line----it's far cheaper to reuse silver, time and again, than to add other types of scrap to the operation. You're better off to sell the scrap copper alloys and buy silver. 

On that note------do not sell pure copper. It's a valuable asset in refining---it's the way you recover your silver. Avoid using wire-----you'll likely eventually end up with a melting furnace that will permit you to melt it and cast large bars that you'll use for silver recovery. I used to do that routinely, using old buss bar from which silver contacts had been removed. That way the small amount of silver that was left behind in the way of silver solder or silver plating on the copper was recovered as the copper replaced silver in solution. In the end, you can even recover the copper if desired, using scrap steel. Don't use aluminum-----sell it for scrap----it's worth a lot more than steel. Or, use it to convert silver chloride to elemental silver. There is no easier way. 



> I have the silver and it's no problem to go with straight sterling (silver and copper alloy typically). I noticed while I was making the tutorial on separating gold from silver how easily nitric chews thru silver, much easier than copper or brass.



Exactly! Just keep applying that logic and you'll enjoy outstanding success. 

American silver coinage is 90% silver. Canadian silver coinage is typically 80% silver. You already know that sterling is 92.5% silver, balance copper. Foreign flatware is often less than sterling, so it is not referenced as sterling. It's not uncommon to find flatware that is as low as 72% silver, but higher tends to be the norm. Scandinavian countries appeared to favor a much lower silver content, so always check them for silver, even when they don't say they're sterling. Look for numbers, anything with three digits should be suspect. Examples might be 720, 850, or 925 (Sterling). If in doubt, file a notch in the object with the corner of a file. Apply a drop of nitric acid to the filed notch. If it doesn't turn green almost instantly, it very well may be silver. If it does, it's plated. Time is critical in this test. Left to stand long enough, if it is silver, the traces of copper included will eventually turn your solution green. It's that first reaction to watch. 

Are you familiar with silver testing solution? We can talk about that if you wish. It's a fool-proof way to test for the presence of silver, and can even be used to a minor degree in determining percentage, although I never relied on it for that. 



> Should I cornflake the gold/silver alloy before using the acid on it?



Absolutely! That breaks it down to large surface areas and thin cross sections, insuring that everything will properly digest in a timely fashion. That may not be an issue if you're just refining for pleasure, but when you have a hot plate covered with beakers of customer gold, you have to make time. Besides, Hoke recommends it!  



> You mentioned using AR in the inquarting process, everywhere else I've read mentions dilute nitric, which is the most efficient?



I'm sorry, I may have said something that doesn't have great continuity. Rather than go back and try to find what I said, let me say it here, properly. Once you have inquarted your gold and poured it into water to make the "corn flakes" I like to mention, the next operation is to apply nitric acid and water. Tap water is very acceptable. You'll generate a tiny amount of silver chloride, but that will not be lost-----it will appear somewhere in the operation and eventually be recovered. DO NOT apply AR. Because of the presence of silver, you won't accomplish anything aside from cleaning your shot very well! 

While it works somewhat faster, pure nitric (reagent grade) is not the best choice. Here's a great little demonstration of why not. I made my own electrolyte for my silver parting cell. I started with 30 ounces of pure silver crystal, product of a previous refining. That was placed in a 4000 ml beaker, then nitric acid applied. While I had reagent grade, I used a tech grade for almost all operations, reserving the much more expensive reagent grade for use in standard and testing solutions. Modern production methods pretty much insure that nitric is not polluted with chlorine, which would be your chief concern. Remember that I did everything in a fume hood and on a hot plate. Once the acid was added to the silver, it did very little. However, the moment I added water (distilled, of need), the silver immediately started to dissolve. 

It has been explained to me that when water is added to nitric acid, hydrogen from the added water provides the necessary hydrogen to form the hydronium ion. That not only accelerates the dissolution, but also extends the capacity of the acid. Economically speaking, dollar for dollar, tech grade nitric will outperform reagent grade. 



> Lastly, is a second dissolution of the gold an absolute requirement?



Absolute requirement? 

No, it is not. If you do your work well, removing anything that will dissolve in nitric before going to AR, you can precipitate gold of good quality from a single refining. Something in me made me do otherwise, and part of the reason was that I processed filings without melting them. The yield was always quite dirty, but good enough to determine an accurate yield, which became the basis for settlement for the customer. That gold, after melting to form a button, was then used as my added gold when refining, during the evaporation process to remove nitric. 

You'll know if you should re-refine, or not, when you melt your gold. When it's pure, there is no sign of frosting on the surface, the color is an astounding gold one, there is no discoloration (oxidation), and if you pour an ingot and don't apply heat as it cools, it will pull a very deep pipe. If you intend to market your gold as industry standard purity, I'd strongly advise that you refine a second time. You'll be amazed to see signs of copper and other elements in the solution after the gold had been precipitated. 

If you choose to not do so, and you sell to other refiners, that's what they'll do with it, anyway, so no need. The decision is yours------there is no right or wrong answer, depending on your objective. Mine was to be known as the best damned refiner the customer had ever used!  

Harold

Edit: changed the word slower to faster---and added the phrase Economically speaking, dollar for dollar, tech grade nitric will outperform reagent grade.


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## lazersteve (Mar 27, 2007)

Excellent answers, straight to the point, now this is a real forum!

I'm interested in the silver testing solution.. I want to do this right on my next go around.


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