# I think I need direction..



## joon5225 (Dec 7, 2012)

Hello,

First I'd like to thank everyone for this board. I've found it to be very informative, and quite fun to read. 

I've tried my hand at cementing silver with copper, and my very first attempt was a success (got about 1 toz), but my second and third were not so good. I suspect that one of the scraps which I had thought was sterling silver, contained some other element, and contaminated the nitric solution. After dissolving the scrap sterling, using the usual nitric acid + distilled water (calculated based on message board's suggestions), then adding in copper wires, I ended up with much less silver precipitate than I had expected (appx. 10% of scrap mass). After precipitating, the solution is now aqua in color, and not blue like my first trial run. I've tried searching for "aqua" on this forum, but of course aqua regia is all that I seem to find.. Any help would be greatly appreciated.


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## joon5225 (Dec 7, 2012)

Here's a pic of what the remainder of the precipitate looks like. Mind you, there should be at least 11 troy ounces of silver in there. The clumps are silver forming on the copper wires used.


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## joon5225 (Dec 7, 2012)

Semi-decantered solution


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## butcher (Dec 7, 2012)

When cementing silver from a solution containing silver nitrate several things can affect how the process proceeds, too concentrated of a solution seems to slow or stop, or if the solution is not at least a little bit acidic the solution can seem to take forever.
Having the copper where you can stir it, or use a fiberglass or glass stir rod and knock the silver off of the copper exposing more copper to solution, otherwise you silver solution will have a hard time penetrating the thick build up of silver on the copper, also this is a contact reaction where the silver ions in solution need to come into contact with the copper atoms to gain an electrons from the copper, stirring and fresh exposure to copper can help reduce more silver atoms as they receive an electron from the copper atom.
Surface area of the copper, the more surface area of copper that these silver ions can get to the better and easier to transfer electrons form all of those tiny atoms in the copper to the silver atoms in solution .

Do you think you still have silver in solution? Check it, decant a little of the nitrate solution out into a small test vessel, and add some HCl see if you get silver chloride (milky white solution or white curds).

Note palladium can cement after silver and HCL will not detect palladium,
but DMG will test for palladium and give a yellow precipitant.


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## nickvc (Dec 8, 2012)

If you don't have hydrochloric you can use table salt to check the sample of nitrate solution for silver.


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## joon5225 (Dec 8, 2012)

Thank you for the replies. 

Butcher: I'm reasonably certain there is still a lot of silver left in the solution. I've put 400 grams of sterling + 400 ml of 67% HNO3 + 400 ml of distilled water in total. I don't have HCL or DMG on hand, so I went with Nick's suggestion and I see the following (please see pic). Does this mean I have to go with the silver chloride method? I was trying to avoid that since the cementation method seemed to be quicker.


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## nickvc (Dec 8, 2012)

The problem may well be that your copper is getting covered in the silver cement, try using sheet or opened up copper pipe which can be moved to allow the silver to drop off thus allowing the silver nitrate solution access to the copper to cement further silver from your solution.


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## Palladium (Dec 8, 2012)

It takes about 1.5ml of nitric to dissolve a gram of sterling silver. Going by those numbers it would have taken you 600 ml of nitric to dissolve 400 grams of sterling.


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## joon5225 (Dec 8, 2012)

That is actually what I had intended. I wanted to be left with some sterling left over for the next batch, that way I would know that all of the nitric acid was spent. Maybe that was the problem? 



Palladium said:


> It takes about 1.5ml of nitric to dissolve a gram of sterling silver. Going by those numbers it would have taken you 600 ml of nitric to dissolve 400 grams of sterling.


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## butcher (Dec 8, 2012)

the silver chloride in your test showed silver.

Is the solution dilute enough?
Is it acidic enough (just a little free nitric)?
Is there enough surface area of clean copper?
Is there good circulation of the solution to come into contact with the copper?
Is the solution free of Chloride which may crust over the copper with silver chloride if the solution was not acidic enough?


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## MysticColby (Dec 11, 2012)

Is there enough copper? 400g sterling would require about 117 g copper to cement 370g silver
Yeah, stirring / dislodging the cemented silver from the copper is absolutely necessary


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## kadriver (Dec 14, 2012)

joon5225 said:


> That is actually what I had intended. I wanted to be left with some sterling left over for the next batch, that way I would know that all of the nitric acid was spent. Maybe that was the problem?
> 
> 
> 
> ...



joon5225:

Having some silver left over is a good way to go, it ensures all your nitric gets used up and there won't be a large amount of nitric left over.

If you were to add 600ml (1.5ml nitric X 400 grams sterling/925 silver) of nitric acid to 400 grams of sterling then chances are high that you would have excess nitric when the reaction is complete.

Instead, add your nitric acid incrementally rather than using a given number to disgest your silver.

Excess nitric causes problems when you go to cement the silver with copper;

1) excess nitric consumes the copper quickly
2) excess nitric will re-dissolve your cement silver as fast as it cements out
3) poison fumes (visible red/brown fumes) will be emitted from the cementation process
4) the silver will become bloated with fumes and tend to float
5) the cement silver will turn to a fine mud that is hard to rinse

To avoid all this, first TEST ALL YOUR SILVER before commiting it to the nitric acid reaction vessel.

Once you are certain that all your metal is silver, weight it and record the weight.

Use this number and add that amount of DISTILLED WATER to your reaction vessel - if you have 400 grams of tested sterling/925 silver, then add 400ml distilled water.

I use a heavy pyrex coffee pot with a fitted lid. Then incinerate each piece of silver with a MAPP (or propane) torch. Heat EACH PIECE to redness with the torch.

Once you heat a piece to redness, then drop it into the distilled water in your reaction vessel and repeat until each piece of silver has been annealed.

Once all the silver has been annealed (heated to redness then doused in the water) then place the vessel on low heat and begin adding small amounts of nitric acid.

Start by adding 50ml of acid to the 400 grams of silver and 400ml of distilled water. Put the lid on and watch - there will be bubbling and red/brown fumes.

When this calms down and the fumes begin to lighten up, add some more acid.

Incremental nitric additions ensures that you won't overshoot and end up with excess nitric in your silver nitrate solution.

In my opinionm it is best to end up with the liquid at or near boiling, no more fumes being produced, and a few pieces of undigested silver in the bottom of the vessel.

When you add copper to the liquid that has been prepared in this way, the cement silver will be small granules and have a crystaline look and be easy to rinse.

Sometimes the nitric gets completely used up - some free nitric is required to cement the silver.

If the copper just sits in the silver nitrate and no silver cements, then add a few drops of nitric and stir. The cementing will then begin.

kadriver


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## kadriver (Dec 14, 2012)

Also, if your silver nitrate is highly concentrated then the silver will passivate on your copper.

Passvation is when the silver is so concntrated that it forms a hard crust on the copper and prevents fresh silver nitrate from contacting the clean copper inside.

Once the silver crust is formed I have found that it is kind of difficult ot get it off the copper.

To avoid this, I usually dilute my final filtered silver nitrate solution with an equal volume of DISTILLED water.

This eliminates the passivation and makes some nice looking cement silver.

Also, if you are careful and remove the copper before it starts to disintigrate and drop tiny bits of copper in your cement silver, then you will get some nice clean silver that is very near three nines fine.

But other metals will cement out with the silver and contaminate it so we can never count on silver cemented with copper to be three nines fine - it must be run through an electrolytic silver cell first.

Edited once to add a word

kadriver


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