how to guestimate the purity when the button is over 22k

[ericrm]

the title says it all
how do we guess when over 22k
when melted together ,does silver and gold alloy make an oxidation layer on top of the button
if i have a 95% pure button contaminate with silver ,will the silver form some sort of uglyness on the top of the button?

 

[glondor]

http://www.belleaircoins.com/how-to-test-for-precious-metals-2/



TEST FOR 21 TO 24K GOLD: Assaying 21-24K is the most difficult of all tests. The best way is to rub a streak from a known 21 or 22K coin and a streak of the unknown, side by side. Apply 22K or platinum acid. The lower karat metal will fade first. This takes some practice and educated guessing. If the item tested is said to be 24K rub it on the stone. If you get a nice smooth even streak it is not 24K. Pure gold will not “bite” into the stone. It will be impossible to get a nice even streak and might leave little flecks of gold on the stone.

 

[NobleMetalWorks]

Gold and silver are different weights. If you don't have a homogenous melt, then when you pour a bar the gold will tend to want to sink to the bottom of the bar, and the silver will be forced to the top. If your melt was homogenous, then you still might have some of that, but not likely.

If your bar is how you described I would guess it's because it wasn't melted properly. But I am just assuming. It also might be that there is slag associated on the top, other base metals that were not picked up by your flux, or maybe flux also.

If your button is not very big, it wouldn't take much silver to upgrade the silver content then dissolve in Nitric Acid which would leave your gold behind and you could process accordingly.

Or if you don't have the silver, since the majority is gold, you could dissolve the gold in AR, the silver would convert to AgCl or Silver Chloride, so long as you are willing to reduce the AgCl this might be a good option for you.

Why are you not trying to remove the silver instead of leaving alloyed with Au?

if you want to test for gold content you could get it scanned by XRF, make sure that the top, sides and bottom are scanned, if your melt was not homogenous, then the readings will be different. If I was going to get it scanned by XRF, I would re-melt and make sure it was homogenous.

Trying to do an acid test on anything above 22k is difficult at best. Gold of high purity tends to smear on the scratch stone and doesn't lend to being tested very easy at all.

Scott

 

[ericrm]

no the main reason is because here in quebec having acces to an xrf alone is difficult, imagine having to find an xrf well calibrated when you just need to know about a single button.
i never heard of a jeweller being able to recognise a 24k gold button for what it is. so that make me think on how to recognise an refinned but still impure button.
i would think that a unpure button of gold and copper will most likely make some kind of oxide layer (since copper is realy easily oxidized but does silver do the same?

 

[NobleMetalWorks]

Silver oxidizes, this is why it tarnishes, and also why it's not used in electronics, gold is used instead for this very reason.

But you are guessing, would you really run the risk of guessing when you are selling? If you under guess you get ripped off, if you over guess you will not sell. It's better if you refine it further so you can be assured of purity.

Who are you going to sell it to, won't they do an XRF at the very least? You could also fire assay it since you don't have that much, you will end up with high purity Au doing that as well.

Trying to figure out a way to guess at what might be going on in your gold material is kind of the backwards way of doing things. Just process it for high purity then you don't have to worry about what else might be included. Also consider this, whoever might purchase from you is going to see what your bar looks like, and try to way undervalue your Au because of this fact.

Scott

 

[MysticColby]

metallic silver does not oxidize in air at room temp. tarnish is silver sulfate, caused by minute amounts of hydrogen sulfide in the air (if you live near a ocean, there's more hydrogen sulfide, so it tarnishes quicker)
similar to oxidizing, but not the same.
if you happen to have silver oxide (by reacting silver chloride with sodium hydroxide, which then breaks down into silver oxide, for example), you can convert it to silver and oxygen by heating it to 280ºC. Which is why you won't get silver oxide formed when you melt silver

 

[goldsilverpro]

Specific gravity done accurately. The S.G. of a typical (91.67Au - 5Ag - 2Cu - 1.33Zn) yellow 22K alloy is about 17.7. The S.G. of 24K is 19.3.