# Gold purity 99.9 % but the color of gold is greyish when heated



## refiningguy (May 8, 2022)

Hello guys ,
I recently came to know about this amazing forum while searching for gold refining methods . 
Could you guys please direct me into the right direction
i recently refined some gold and it came out good with a purity of 99.90 % . But the problem is that when i heat the gold button and leave it as it is to cool down , the color of the gold is grey. And when i heat it and pour it in water ( when its still hot ) its the normal yellow color of gold . Can you guys please tell me why could this be happening .
I first dissolved the 91 % gold in Aqua regia . Then i poured some urea . After filtering i precipitated it with a gold reagent . 

I would be highly thankful to u guys if you could help me .

Thank you


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## Lightspeed (May 8, 2022)

Acetylene torches can discolour gold in my experience, even if its of good purity. Dirty Flame if it is not tuned correctly, think Carbon excess.
Instead of directing the flame onto the metal directly try radiated heat, thats one possibility.
Why it is cleaner when turning to shot is strange but sounds like a surface contaminant on the metal which is shed on contact with the water.

Are you using the same method of heating when turning to shot as you are when just turning to a blob?

What type of crucible? borax lined quartz silica melt dish? the borax should be keeping the surface clean of carbon, so sounds strange

Where did you get the assay for 3N? was it XRF?

Sounds like it may have something to do with the instant cool into water versus slow cool in the air, also sounds like a definite contamination of some sort, pure metal in a melt dish looks like a mirror and should be free of any surface contaminants as its spinning in the melt dish, contaminants are easily visible.

Attach a few pictures of your metal shot and blob so we can see the difference.


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## Yggdrasil (May 8, 2022)

refiningguy said:


> Hello guys ,
> I recently came to know about this amazing forum while searching for gold refining methods .
> Could you guys please direct me into the right direction
> i recently refined some gold and it came out good with a purity of 99.90 % . But the problem is that when i heat the gold button and leave it as it is to cool down , the color of the gold is grey. And when i heat it and pour it in water ( when its still hot ) its the normal yellow color of gold . Can you guys please tell me why could this be happening .
> ...


There is some info lacking here:
What was the source?
How do you know the purity, before and after refining?
Why did you use Urea?
Which Gold reagent (precipitant)?
How did you melt it?
With or without Borax?

And please do not use lingo like u here.


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## refiningguy (May 9, 2022)

Lightspeed said:


> Acetylene torches can discolour gold in my experience, even if its of good purity. Dirty Flame if it is not tuned correctly, think Carbon excess.
> Instead of directing the flame onto the metal directly try radiated heat, thats one possibility.
> Why it is cleaner when turning to shot is strange but sounds like a surface contaminant on the metal which is shed on contact with the water.
> 
> ...


Thanks for replying ,
I am using the same method of heating everytime , thats why i am certain that its not because of heating
i got it assayed through xrf
I am attaching the picture . The one on the left is heated without dipping in water and without using borax , and the other one is after turning it to shot.
Both the pieces are of the same metal refined.

Thanks


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## Yggdrasil (May 9, 2022)

Then it more or less has to be a coating. 
How and where do you melt your buttons.
There is no way pure gold in a clean crucible would look like that.

And you have not answered the questions on the source.
XRFs are not better than the sum of the operator and the libraries.
There are more questions not answered either so please do so we understand what is going on.


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## refiningguy (May 9, 2022)

Yggdrasil said:


> There is some info lacking here:
> What was the source?
> How do you know the purity, before and after refining?
> Why did you use Urea?
> ...


Thanks for replying

Source was old jewellery
purity was tested before and after on xrf machine
to remove excess nitric acid from AR
i am not sure which gold reagent i am using probably SMB or Ferrous sulphate in liquid form ( when dropping the precipitant into the AR , the precipitant turns black on contact with the AR )
i would be grateful if you or someone else could tell me which precipitant it could be
i melted the jewellery and the refined metal in a graphite crucible using little borax
both the small buttons of gold are a part of the metal refined which i heated using LPG flame


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## Yggdrasil (May 9, 2022)

Then I think most is sorted out.

Urea are not much used here anymore due to two reasons.
Under certain conditions it can form an explosive compound. 
Though it removes the NOXes form the leach it do not remove Nitric itself.
Sulfamic acid (grout cleaner) do both and in turn creates sulfuric which pulls any traces of lead out of solution.

Which color was the precipitant, and what color was left in the solution after?

And now I think we have the culprit.
Graphite do NOT like borax so by using borax in the graphite crucible you have dissolved some carbon which is coating your button.
When you put it into water when warm the borax/carbon coating cracks off.
When cooling slowly it don't. Gold do not need borax during melting.
Use a common melt dish and dress(coat) it in borax and then use without.


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## Shark (May 9, 2022)

Copperas (ferrous sulfate) will turn the solution almost black when dropping gold.


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## 4metals (May 9, 2022)

Put the discolored shot piece in Hydrochloric Acid, if it’s copper it will dissolve. That’s what I suspect. But just dipping it all in Hydrochloric Acid won’t solve the problem. A second digestion and drop will.


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## Lightspeed (May 10, 2022)

Yggdrasil said:


> Then I think most is sorted out.
> 
> Urea are not much used here anymore due to two reasons.
> Under certain conditions it can form an explosive compound.
> ...



I am going with the use of Borax in a graphite crucible, your metal needs to be re -refined now, it will be contaminated with Carbon Graphite throughout.

You could possibly clean it in a Quartz Silica melt dish lined with borax, but if it were me i would simply put it down as a learning curve of what not to do when you melt your refined metals and re digest and re-refine, all the metal, including whatever has been turned to shot despite it being more gold in colour will also be contaminated with carbon graphite and using it for jewelry will create more problems as the carbon will prevent good solder adhesion, it may also reveal itself to be brittle due to carbon impurities and these issues will be more evident as you progress with working the metal.


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## refiningguy (May 11, 2022)

Yggdrasil said:


> Then I think most is sorted out.
> 
> Urea are not much used here anymore due to two reasons.
> Under certain conditions it can form an explosive compound.
> ...


thanks for replying
i will try to use Sulfamic acid next time instead of urea .
precipitant is a clear liquid , a little milky i guess
i will keep the borax away from the graphite for the time being , and i will experiment a little to see if adding borax to graphite resulted in change in color and i will update it here once i do so.

thank you for sharing your knowledge with me


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## refiningguy (May 11, 2022)

Shark said:


> Copperas (ferrous sulfate) will turn the solution almost black when dropping gold.


thanks for replying and sharing your knowledge


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## refiningguy (May 11, 2022)

4metals said:


> Put the discolored shot piece in Hydrochloric Acid, if it’s copper it will dissolve. That’s what I suspect. But just dipping it all in Hydrochloric Acid won’t solve the problem. A second digestion and drop will.


thanks for replying
won't some of the gold ( even if its very little ) will also dissolve in Hydrochloric acid.

Thank you for sharing your knowledge with me.


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## refiningguy (May 11, 2022)

Lightspeed said:


> I am going with the use of Borax in a graphite crucible, your metal needs to be re -refined now, it will be contaminated with Carbon Graphite throughout.
> 
> You could possibly clean it in a Quartz Silica melt dish lined with borax, but if it were me i would simply put it down as a learning curve of what not to do when you melt your refined metals and re digest and re-refine, all the metal, including whatever has been turned to shot despite it being more gold in colour will also be contaminated with carbon graphite and using it for jewelry will create more problems as the carbon will prevent good solder adhesion, it may also reveal itself to be brittle due to carbon impurities and these issues will be more evident as you progress with working the metal.


thank you for replying and sharing your knowledge with me .
I will use Silica melt dish lined with borax next time and will keep borax away from graphite.


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## orvi (May 11, 2022)

Did you measured the button personally or let someone measure it ? This is not the standard behavior of gold. I suspect that the XRF gun maybe shown 99,9%, but it came with big standard deviation of measurement, which could hide some impurities. It is fairly common to see folks claiming 99,9% gold with 2sigma value of 2,5 etc


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## Shark (May 11, 2022)

Impurities in your melted gold will often show up as a different color moving around on the surface of the molten gold. When it cool’s quickly it will often shed the surface impurities. When I have such buttons of gold I do as 4metals suggested. This takes out that much of the impurities when I process the next refine, thereby not adding more “trash” to the AR than I have to. Often, the cleaner the gold the smaller this off color will be when it is the melted state. I see this most often when I melt in a well used dish, picking up small bits of other metals from multiply melts. 

Anytime I have a problem I refine it again and use a clean melting dish. As for graphite molds I have no experience with them, but the consensus has always been to not use borax in them.


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## 4metals (May 11, 2022)

There is an old technique called toughening which is used on refined gold to remove that surface discoloration you see on the surface of the molten gold that Shark just mentioned. 

First have a dedicated crucible for melting refined gold, no sense refining only to add impurities when you melt it. If you see the surface film add one or 2 prills of niter (KNO3). The niter will bounce around on the surface and grab the base metals by oxidizing them. If you add just a pinch of borax you will make a stick spot which will stick to the crucible wall and collect all of the dancing about metal oxides it contacts. This is a finesse technique so use very little of the niter and borax.

This can often take care of the issue while the gold is molten and eliminate a Hydrochloric Acid dip.


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## kurtak (May 11, 2022)

Lightspeed said:


> You could possibly clean it in a Quartz Silica melt dish lined with borax,


He needs to understand that this "lining" is a process of "glazing" the melting dish (not just putting a layer of powdered borax in the dish before putting the gold in the dish on top of the powder)

I don't have time to post the "glazing" process - so hope someone else can/will

Kurt


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## Martijn (May 11, 2022)




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## 4metals (May 11, 2022)

I have never melted reined gold in a borax glazed crucible, always clay graphite. I think that, in time, a borax glazed melting dish will take on a colored hue from the metal oxides the niter helps remove. That may in time put, or at least expose molten gold to impurities that weren't there when you started. 

I always closely inspected my fine gold crucible and chipped off any borax I saw which was holding those oxides. By using an ever so small quantity of borax it tends to stay in one spot on the diameter of the crucible at the level of the molten gold. 

I think a glazed melting dish would encourage the oxides to stick anywhere there is borax and make the dish unacceptable for fine gold melts. It's still fine for karat melts or anything you will be refining after melting.


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## grainsofgold (May 31, 2022)

You can soak the button in jewelers pickle this will clean the surface. Best to do once the button hardens and is still hit drop it in warmed pickle. sparex is a brand of pickle , some use Ph down used fir swing pools. 

Once the surface is cleaned re melt it in a clean crucible with a clean flame from your torch and then see how it turns out. If the surface dark re refine it.


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