xrf analysis

[goldorack]

Hello all,

I got really fustrated not really knowing what I start with when (very small scale) refining so I finally got my xrf. I had purchased rings and a few coins from different sources such as auctions. This evening I analysed about 10 pieces and found a few surprises. (Unsurprisingly a small coin that I purchased as 21 K was actually 18 K).

First none of the 10 K rings were actually 10 k - they ranged from 9 to 9.5 K - which explains why my yield was not as expected. Does anyone has similar results?

My gold (purified according to methods described in this forum) was 99.7 percent pure with some silver contamination so I need to work on that.

Biggest surprise was that most of the rings have a big Cupper content. A few contain over 40 percent cupper then gold about 38 percent , the rest is Nickel and Silver . This is yellow , not rose gold. I was really surprised by that. Any comments? Also do you need to inquart if silver content is below or around 10 % ?

This is getting more and more interesting for me. I am working on a reactor now.

 

[FrugalRefiner]

First none of the 10 K rings were actually 10 k - they ranged from 9 to 9.5 K - which explains why my yield was not as expected. Does anyone has similar results?

In the US, there was a lenient allowance for most of our history. The allowances go back to times when small jewelers didn't have the technology to guarantee exact tolerances. A cast piece of jewelry was allowed to be up to 1/2 karat below what it was marked. If the item included solder, an additional allowance of another 1/2 karat was given. The tolerance was tightened in 1981, but since I don't know when a piece was made, I always assume 1 karat under any stamped value.

My gold (purified according to methods described in this forum) was 99.7 percent pure with some silver contamination so I need to work on that.

Once your gold is dissolved, add 2 to 3 times its volume in ice. A small amount of silver can be dissolved in strong, hot AR. Dilution and cooling will cause it to become less soluble. Filter and drop your gold.

Biggest surprise was that most of the rings have a big Cupper content. A few contain over 40 percent cupper then gold about 38 percent , the rest is Nickel and Silver . This is yellow , not rose gold. I was really surprised by that. Any comments? Also do you need to inquart if silver content is below or around 10 % ?

Usually not. But if there is any chance of PGMs being present, inquarting can remove them before dissolving the gold, making overall separation a little easier.

Dave

 

[nickvc]

10 k and below could be described as a copper allow rather than gold if red or yellow alloys, the make up of 9k yellow is if plum 37.5% Au 10-12% Ag the balance been copper with a small percentage of zinc, that’s the English alloy, if Italian no silver and more copper and zinc. Nickel is/was usually used in white gold but with allergies been a problem for some many stopped using it. Any British hallmarked items will be plum or above while as Dave pointed out US alloys can be 1k below, I’m not sure of the rules for Canada.
Most 14k and above can be directly dissolved in AR as the silver content is normally low but for any PGM bearing alloys or settings inquarting is for most the best step as Dave pointed out with the reason above.
For most inquarting is by far the safest method to ensure the gold can be precipitated at a high purity, I will say that a second filtering through the used filter helps remove most silver chloride but you do need to cool and dilute the solution first hence why Dave advised using ice.

 

[olawlor]

10 karat gold usually has a lot of copper so that it looks gold colored. Only 40% gold mixed with white metals like silver or zinc makes an alloy that basically looks white (perhaps a very pale green).

 

[goldorack]

I want to thank FrugalRefiner, Nickvc and Olawlor for the comments - and actually this forum- which really make me understand more and more about the processes involved. I will post as soon as I get more results. Diluting gold containing AR with ice (to precipitate silver) before filtering is something I have avoided mainly because I was afraid to end up with a dilute AR solution that might result in colloidal gold precipitate. I will try it next time. Thank you all.

 

[grainsofgold]

i’m a jeweler. Karat stamps are a starting point. XRF only reads the top surface skin. if stones are pulled out melt mix will and pour into a B shaped mold and take an average. Closer to what you have then just a surface read.

 

[goldorack]

Grainsofgold thank you for your comment. Yes I am well aware of the xrf reading just the surface. I do not want to destroy the rings so I am not aware of any other way. If you know any other technique please let me know. I am also wondering in your experience how much can you trust the karat stamp. I have come across quite a bit of forgeries, some easy to see. but my question is (assuming it is not a forgery) regarding the 10 k mark. They all tested 9 to 9.5.