# Question about Cementation



## RicRock (Mar 6, 2013)

Hello,

I started processing some sterling silver using homemade nitric as seen in this post:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=17508

I began cementing with a piece of copper tubing and wasn't what I expected from my readings or videos viewed.

I wasn't expecting the cemented silver to float. The solution was very diluted with distilled water and it was under heat so maybe the convection currents?













and a short video:

http://youtu.be/G9ZO6swmMJ4

Is this correct?


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## Anonymous (Mar 6, 2013)

That's normal, from my experience. Just let the copper sit in there and it'll eventually drop to the bottom.

Also, it's best to use flat bar. If a pipe is all you have (Like I do,) try to cut it open lengthways. If that's not possible, make sure the copper is either new or very clean, and tap on it often, with another piece of metal from the top, so that way you can release any silver that builds up on the inside of it.

Also, if you're not in a rush to get the silver, I wouldn't apply heat to speed up the process. I noticed that when I do that, the solution gets a dark greenish/blueish color, and that I believe the nitric is attacking the copper much faster.

Kevin


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## 4metals (Mar 6, 2013)

You can also flatten copper pipe and it works well, a few passes through a rolling mill will give you flat stock. if you're short 1 rolling mill you can always beat it to death with a sledge hammer on an anvil and get the same result.


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## Anonymous (Mar 6, 2013)

4metals said:


> You can also flatten copper pipe and it works well, a few passes through a rolling mill will give you flat stock. if you're short 1 rolling mill you can always beat it to death with a sledge hammer on an anvil and get the same result.


Everyone keeps coming up with great ideas I never thought of. That makes sense too. I can cut the pipe to the length I need, then flatten it with a pipe wrench to at least close one end, then flatten it all the way down.

Oh yeah. I have plenty of new pipe I can use. *4metals*, where were you when I was hack sawing, using Dremel tools and even my zip saw to split open my copper pipes? :mrgreen: 

This is great to know! Thanks!

Kevin


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## RicRock (Mar 6, 2013)

Thanks for the info, very glad it's normal.

Great ideas on flattening the pipe or opening the pipe!


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## kadriver (Mar 6, 2013)

I have had this happen. It is due to excess nitric in your silver nitrate solution.

The cement silver begins to dissolve as fast as it cements out (because there is excess free nitric in with the silver nitrate).

As the cement silver begins to dissolve it generates noxx gas that bloats the cement silver and causes the cement silver to float to the service.

To solve this add a spoon of urea - be careful because if there is lots of excess nitric then the solution could boil over.

Put your container inside a casserole dish to catch any overflow in case this happens.

The best way to avoid this is to use just enough nitric acid to dissolve your silver and no more.

I like to have a few pieces of undissolved 925/sterling left over after the reaction has ceased (no more red fumes).

This ensures that all the nitric has been consumed. Your cement silver will have a nice crystalline structure that is easy to clean.

Excess nitric causes the cement silver to become very fine mud that is hard to clean.

It is possible to consume the nitric so completely that the copper will just sit there and no silver will cement (a small amount of free nitric is required). If this happens just add 3 or 4 drops of nitric acid and stir to get the cement action process started.

kadriver


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## goldsilverpro (Mar 6, 2013)

I think the main problem with copper tubing is that the silver will cement on the inside of the tubing. Flattening, of course, will solve the problem. Another solution would be, after rinsing, to use a long bottle brush to scrub the inside of the tubing. A lab buret brush would work for this.


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## etack (Mar 6, 2013)

One thing to note also is you have to much in your container.. When you are cementing it can and will release gasses that carry with it some silver nitrate. you will see it all over the out side of your container tomorrow when it dries and light hits it. Give yourself some room to move. :lol: 

Eric


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## mikeinkaty (Mar 6, 2013)

I found some 3" diameter, 1/8" wall, copper pipe at a scrap metal place. I had to soak the inside with dilute HCL to get rid of the lime buildup but that went pretty quick. I used a 3" wire brush in my electric drill to get the inside shiny. Each piece is about 10" +/- long and I just set them vertically in my cementing bucket as is. Go by occasionally and shake them out. Didn't hammer them out. Also picked up 11 lbs of buss bar. All that surface area on the 3" pipes really makes the drop fast. I use a taller bucket as the reaction is faster.

Kadriver - I always make sure the sterling dissolve is finished with pieces left in the jars before dropping. I also filter the solution before dropping. But, I generally get real fine mud. Haven't figured that out yet. I have gotten the floating cement but rarely and not much of it. I generally stir it up and don't see it any more.

Mike


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## RicRock (Mar 7, 2013)

Thanks to all.

Pic of my first cemented silver:


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## Anonymous (Mar 7, 2013)

Looks nice. Make sure you give it a good (3 at least) hot or boiling distilled water rinses before drying and melting.

Kevin


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## mikeinkaty (Mar 7, 2013)

What Testerman says plus I would test the rinse water with household ammonia. Catch a little of the rinse water after the 3rd rinse in a test tube or small beaker and put a few drops of ammonia in it. If it turns blue then do a couple more rinses. Turning blue means there is still copper in the cemented silver. Holding the beaker up to a white sheet of paper will help see the blue. Then do the same thing when rinsing crystals if you have a cell. Crystals generally rinse pretty quickly. 

Mike


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## Anonymous (Mar 7, 2013)

mikeinkaty said:


> What Testerman says plus I would test the rinse water with household ammonia. Catch a little of the rinse water after the 3rd rinse in a test tube or small beaker and put a few drops of ammonia in it. If it turns blue then do a couple more rinses. Turning blue means there is still copper in the cemented silver. Holding the beaker up to a white sheet of paper will help see the blue. Then do the same thing when rinsing crystals if you have a cell. Crystals generally rinse pretty quickly.
> 
> Mike


Thanks for that info Mike, because I never done that before. It makes sense and I'll remember to do that for now on.

Kevin


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## kadriver (Mar 10, 2013)

To get the best result, use two beakers - one with just water and the other with the wash water to be tested with ammonia.

After you add the ammonia, set it next to the beaker with just water and compare the two - keep rinsing until they both appear identical. The washer water can "look" clear, but still have a slight tint to it.

Setting it next to the clean water will reveal the slight tint that your eye will miss - another Goldsilverpro tip.

kadriver


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