Where did the gold go?

[Kasse]

We had 2 grams of gold. It sat I water for a week and turned black. I put the gold into a melting dish with borax and melted into a bead about 12mm in size. Put the bead into a cuppel with 3 grams lead into the furnace at 1700. Came back in 40 minutes. And there was nothing in the cuppel. Not gold no red lead oxide. The dish if the cuppel was black with no metallics. Split the cuppel and there is a dark gray sparkling layer about 2mm thick, but no gold present. Where did the gold go? Need some help.

 

[haveagojoe]

Gold will evaporate at around 1400C.

 

[Yggdrasil]

We had 2 grams of gold. It sat I water for a week and turned black. I put the gold into a melting dish with borax and melted into a bead about 12mm in size. Put the bead into a cuppel with 3 grams lead into the furnace at 1700. Came back in 40 minutes. And there was nothing in the cuppel. Not gold no red lead oxide. The dish if the cuppel was black with no metallics. Split the cuppel and there is a dark gray sparkling layer about 2mm thick, but no gold present. Where did the gold go? Need some help.

There is not enough information.

Anyway the "Gold" turning black should have been a wake up call.
Gold do not react to any single acid and definitely not Water.
How do you know it was Gold in there in the first place?

How was this Gold achieved.
As detailed as possible please.
Start material, how it was treated and the whole story.

 

[Yggdrasil]

Gold will evaporate at around 1400C.

I suspect he is talking about Farenheit.
And Gold has a boiling point at 2836 Centigrade

 

[haveagojoe]

I suspect he is talking about Farenheit.
And Gold has a boiling point at 2836 Centigrade

i stand corrected

 

[Alondro]

As Yggdrasil said, actual gold will not turn black in water. What I HAVE seen turn black in water (especially if it's hard water that's alkaline) is some aluminum brass alloys.

 

[anachronism]

In fairness, gold going black in water would have set off a few alarm bells.

 

[Kasse]

The gold comes.from our hardrock mine. It was crushed from the gold vain. Jaw crusher into an impact mill then into a nefco bowl. No pretreatment on the gold. Particle size was +30 mesh. There is sulfides trace Telluride's and antimony in the ore. Cons were paned to recover the free gold. It was bright and soft. No discoloration on it. After sitting in the water that it was processed with. The gold had a black coating that could be rinsed off with clean water. I assumed this was from the sulfides braking down. I put the gold pieces into a melting dish with lead to from a bead so it could be cuppeld and pull any base metal's out of the gold. The gold formed a nice bead in the dish, added 5 grams of lead, let it cool then pulled it out of the melting dish and put it on the new cuppel. Furnace was set to 1500f. Put the cuppel into the furnace. I am puzzled as to what happened as I have never had this happen.

 

[Yggdrasil]

I'm not very experienced in cupelling but that seem strange yes.

 

[anachronism]

Thanks for the additional information and pics. This makes it easier to understand.

 

[4metals]

I'm not very experienced in cupelling but that seem strange yes.

Strange indeed. In fire assaying, where I have most of my cupellation experience, a 1/2 gram sample (typically containing 50-60% gold) is cupelled in 15 grams of lead. Approximately a 30:1 ratio. Your 2 grams of gold to 5 grams of lead is a 2.5:1 ratio.

I do not know if that would matter but enough lead to form the pool of metal may be the issue. Even though as the gold in an assay cupels down the lead becomes less and less in the pool. If it was gold there should be something remaining in the cupel at the end. Which begs the question, was it gold?

Were the other properties of the gold material you had gold like? Was it malleable or brittle? Would it leave a line on a scratch plate like gold leaves because of it's hardness?

 

[kurtak]

Strange indeed.

I agree with 4metals - strange indeed

Couple of questions

1) are you using home made cupels or store bought (like from Legend)

2) did you preheat the cupel to temper it (drive out moisture) before putting your lead/gold bead in the cupel

I ask because cupels - like crucibles should be tempered to drive out any moisture in them before putting the lead/gold bead in the cupel

Moisture in the cupel "may" cause "spiting" of the lead/ gold bead when it becomes molten - meaning it may/can cause the molten lead/gold to spit out of the cupel & end up "splattered" around inside the furnace

This would be more so a concern with home made cupels then with store bought cupels as home made cupels could have enough moisture in them to cause the molten lead/gold to literally "explode" out of the cupel

Just a "possibility" if the cupel was not tempered before adding the lead/gold bead

Kurt

 

[4metals]

I ask because cupels - like crucibles should be tempered to drive out any moisture in them before putting the lead/gold bead in the cupel

I always pre heated cupels in a hot furnace before charging them with the lead boats for the exact reason Kurt mentions. When members mention cupellation with a torch how they eliminate moisture is one of the things I think of.



Pre-heating cupels in a furnace is one of those things that is so second nature to me that I often forget to mention it....... just another example of how multiple eyes on a public forum can spot something easily over looked.