Non-Chemical Cleaning Diamonds

[auprecious]

I am very new to the forums and would like to thank everyone for the wonderful information they have shared.
I have done a couple searches and could not find what I was looking for so I decided to post. If this has been discussed already, could someone point me in the right direction?

I am doing daily melts with all types of scrap gold. Some of it being jewelry. While I do pull most of the stones out there are some rather small ones that I have left to get collected and cleaned later. Talking half pointers to maybe 3 and 4 pointers. My question is what is the safest and most effective way to clean these stones. I'm using an electric kiln and after the pour they generally are left in the crucible and I am able to dump them right out. they are, however, covered in graphite and don't clean well. Any suggestions would be greatly appreciated

 

[kuma]

Hello and welcome to the forum!
This is something that I have no experience in whatsoever , but your question has me thinking.
There are some people on the forum that use a Lye ( sodium hydroxide ) solution soak to easily tell their cubic zirconia's from their diamonds.
The theory is that the lye will attack and etch the cubic zirconia , but leaves the diamonds unaffected.
I'm wondering if this would clean up your diamonds and be a route that could maybe help ?
Another possibility is pickling them in Sulphuric Acid , some people do this to freshly poured buttons of precious metals to help remove any glass flux that may be clinging to the surface.
As both of these methods would use potentialy dangerous chemicals , either couldn't count as being " the safest " , but as your already using a kiln and melting scrap gold I feel you should be okay with this.
Again , I have no experience with this , I'm just throwing a couple of ideas out there based on what I have read! :roll:
I've no doubt that someone with knowledge will chirp in with some valuable advice for you on this one ,
All the best with it , and kind regards ,
Chris :mrgreen:

 

[auprecious]

Thanks for the suggestions. I supposes safest wasn't the ideal word here. I do have pretty effective ventilation for the melts. As far as dealing with acids, I don't know very much but I can only imagine its an entirely different beast with the fumes and possible reactions with metals and such.

 

[kuma]

Hello again chief , and no worries!
As I say , I'm not even sure if it's what your after , but I do know that Lye and Sulphuric wont attack diamond so you should be in good stead either way.

I supposes safest wasn't the ideal word here.

Chuckles , I've read that before!
I guess using potentialy dangerous chemicals is about as safe as flying radio controlled planes , it can be good fun and very interesting , but if your not careful , either yourself or an innocent bystander is going to loose a finger or an ear , it's as safe as you care to make it , :roll:

As far as dealing with acids, I don't know very much but I can only imagine its an entirely different beast with the fumes and possible reactions with metals and such.

+1 from me! :lol:
I'm still very much a *noobie* here myself , and as I've said I've no doubt that another member with experience here will chirp in.
Those were just a couple of suggestions based on what I've read concerning diamonds and the chemical pickling of gold , and not my own personal experience.
I just wish I could help you further!
I wish you all the best with it for now , and send my kind regards ,
Chris :mrgreen:

 

[samuel-a]

auprecious

I'm afraid, cleaning your diamonds from flux and debris won't do much, if you notice, they probably get cloudy or etched (from partial burning).
Re-setting them is probably not an option anymore, though they are still diamonds, maybe can be sold for polishing :?:


kuma

Lye solution has very little effect on oxides, molten lye does fuse with oxides.
Molten lye is extremely dangerous but still safer then the alternative... (HF :evil: )

 

[kuma]

Hi Samuel , how are tricks?
I hope your well!

kuma

Lye solution has very little effect on oxides, molten lye does fuse with oxides.
Molten lye is extremely dangerous but still safer then the alternative... (HF :evil: )

I should have remembered that one , molten lye , as I was reading about it recently , thank you for the heads up!
Also , I hear you on the HF , not one for me chief , :evil:
All the very best for now , and kind regards ,
Chris :mrgreen:

 

[Lou]

Lye actually doesn't do much good against zirconia.

 

[kuma]

Hi Lou , how are tricks?
I hope your well!

Lye actually doesn't do much good against zirconia.

I could swear blind that I have read that people use Lye to differentiate between diamonds and zircon , my bad chief! :roll:
All the best for now , and kind regards ,
Chris

Edit , on trying to figure out where I got my lines crossed I came across this post from you Lou ;

"

Diamonds burn, so it's best to chemically remove them. Cubic zirconia is highly refractory and can't be oxidized (burn) like diamond, so they're persistent and often float to the top of the melt. Usually one can get them trapped in the borax if one adds a few pieces of broken pyrex to thicken up the flux to the point where it can be held back with a quartz fork and the alloy poured out from under it.

Many refiners use HF to frost the fake diamonds (CZ) from the real ones which are unaffected. This works quite well if one is in a high throughput environment where individually testing each stone's conductivity would be a lengthy endeavor.

Lou

I'll get there eventualy! :roll: :lol:
Thanks again and all the best chief ,
Chris :mrgreen:

 

[auprecious]

I've found my answer! Many use a 2:1 sulfuric nitric blend and boil the solution for 1-3 minutes. As I'm sure you guys know, this is meant for loose stones, metal will be corroded.
If anyone is familiar with this process and can offer some advice that would be excellent. Also, if anyone is familiar enough to recommend a strainer that would stand up to the acid bath, this would be excellent as well!

 

[Dan Dement]

Auprecious,

Your questions starts out asking how to clean diamonds. I think you mean you melt them and want to clean them after melting them in with the metal. I suggest that on articles that have small stones that you do not want to hand remove is to seperate out these items and send them as a seperate batch and have the stones removed chemically as a separate batch which several refiners offer. Now, it's going to cost you 1-2% to do those which you should recover by getting the diamonds back is a saleable condition. Depending on the quality of the diamonds, you should be able to get from $50 to $200 a carat for these break outs. For us, we remove them by hand but at times have sent them in for chemical removing. Sometimes, you can add lots of borax and recover them with the slag borax but I have not found any foolproof way to recover them in this method and you can burn the diamonds. WE use the dangerous method of frosting that most people to do not want to use. Lots of the cheap Indian "cast in Place" rings diamonds are not worth mutch, we just snip of the shanks and wait until we have enough to make a decent shipment. We just don't buy much of this type of jewelry and the return on these quality of diamonds is very low.

Dan

 

[4metals]

If you are speaking of removing flux from stones remaining in the flux after the metal was melted. If you used borax as the flux it can be dissolved away using heated nitric and water. I like using just the nitric water mix because it can be done in a stainless steel pot. The resulting waste liquor is loaded with dissolved solids and is easily treated with classic pH treatment leaving solids with the hydroxides in the filter press. Stones and gold beads can be picked from the insoluble fraction.

 

[auprecious]

There are many times that it just isn't practical to remove the stones by hand. And I'm certainly not giving up any dollars for removal. So, by torch or kiln, we will melt them with the melee still mounted. For example, on many pieces you can melt away just the prongs and the stones can be pulled away with very little effort. If the stones happen to have been burnt, a couple minutes in the acid bath will clean them right up and get rid of the "frost". Some claim clarity can be improved.

 

[nickvc]

If you smoke the diamonds in the melt no amount of acid cleaning will repair the damage and repolishing is the only option, your saving cents and losing dollars not having them chemically removed and all that messing around. Build a hood and do the job yourself if you want to save mone, it's all outlined here on the forum.

 

[4metals]

And I'm certainly not giving up any dollars for removal. So, by torch or kiln, we will melt them with the melee still mounted. For example, on many pieces you can melt away just the prongs and the stones can be pulled away with very little effort. If the stones happen to have been burnt, a couple minutes in the acid bath will clean them right up and get rid of the "frost".

If you think it is a waste of time paying a refiner to do stone removal for you then do it yourself but with the prices melee is being sold for today your method of heating and cleaning is a huge waste of time and a recipe for ruining stones or lowering their value. Don't be penny wise and pound foolish.

 

[Palladium]

If you clip the settings that the stones are in and run just them in a separate lot you will capture more of the pgm. Most of your pd and pt will be found in the settings and by doing it this way you not only simplify your karat refining procedures but also can recover the values from the pgm group easier as well as your stones. I got 4metals to thank for that advice. Another little trick to be wise to is the nitric / flux process he posted above. Great Tips from a great refiner!

 

[auprecious]

Thanks for all the advice guys. I actually have been removing them myself for some time now. At first I was naive and because of that, I have a few carats of melee that is pretty smokey. I've heard from quite a few guys in the industry that this is a relatively common practice (acid wash). Will post some before and after pics if anyone is interested. Should be doing it this week sometime.