# learning to assay



## solarsmith (May 24, 2017)

I am learning the basics. I can melt and poor into a cone mold using a microwave. now im trying to learn to do a torch cupel. I have a temp sensor on the way as I think Im getting it way to hot and volitizing off most of the pgms. hear are pics from my last try. the last pic is the prill in the center and all of the other pics are beads that slowly formed out of thin air around the rim of the cupel. 




Bryan In Denver Colorado


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## kernels (May 24, 2017)

Not intending to ask a stupid question, but what do you mean you can melt and pour using a microwave ?


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## justinhcase (May 24, 2017)

What you have pictured is splash back not volatiles redepositing.
I have read about some old prospectors using a torch to do a ruff assay in the field but everyone els I know uses a furnace.
The problem with using a torch is that to get it hot enough you have to be pushing quite a lot of fuel and oxygen.
This forms a very high-pressure jet that can throw up value in a spray.
I am working on fire assay and flux for larger hot recoveries.
It is not as easy as it reads, getting the flux just right and leaving it to cook for longer than you think it needs as all part of the game.
My flux is still not flowing as well as I would like but prolonged high-temperature smelting is an interesting process.


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## anachronism (May 24, 2017)

kernels said:


> Not intending to ask a stupid question, but what do you mean you can melt and pour using a microwave ?



I'm not sure of the context that he was using but you can melt gold and metals quite happily in a microwave if you set it up properly.


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## solarsmith (May 24, 2017)

its not splash the torch never actualy hit the bead in the cupel. I had the cupel in a hole in the ceramic fiber board.with the torch clamped so it was aimed at the space inbetween the cupel and the fiber board so the flame would wrap around the base of the cupel. the lead bead never sputered or splashed . it just got shiny and shrank. the only odd efect was an almost constant ribon of colors running across the top of the lead bead.

and I can melt with ease in a microwave trying a link to the microwave smelting video . hope it works. https://goo.gl/photos/YipmWkSRUmJf7wsT8


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## kernels (May 25, 2017)

Great video, thanks for sharing solarsmith

I have absolutely zero first hand experience with cupelation, but I have read a book or two on the subject, so take the following suggestion with a grain of salt . . .

The way that I understand the cupelation process to work is that the cupel does not absorb lead, it absorbs lead-oxide. To get the lead to form lead oxide you only have to heat it to 600 odd degrees Celsius, so if you are vaporizing precious metals or even lead, it sounds like it is way to hot. 

Now I am going to have to look further into this whole microwave smelting thing . . .


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## justinhcase (May 26, 2017)

solarsmith said:


> not splash the torch never actualy hit the bead in the cupel.


I get the same thing with my silver doing anodes, I do not think It is redeposition of volatile's.
More the fine spray being formed by gaseous component's bubbling up through the flux and alloy.
That paired with the convection currents and in my case cyclone effect of my burned imparts enough energy for it to travel quite a bit.
Metal Vapour douse do better in a vacuum and tends to deposit in an even layer.


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## solarsmith (May 29, 2017)

can any one tell me what temps I should use for a gold silver platinum cupel? I just did a cupel in a propane furnace and my lazer temp device was maxing out at 950 f even the out side was reading in the high 800s f. thanks Bryan


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## justinhcase (May 30, 2017)

Shall we try and work something out for our selfs, then someone more informed can help us correct our mistakes.
The gold melting point is 1,064 °C but it flows better close to 1200c and silver M/P is 961.8 °C again flows better at 1200c O.T.A.
Silver's boiling point at atmospheric pressure is Boiling point: 2,162 °C and the golds is 2,700 °C..so you would need quite a heat to vaporize them outside a vacuum.
Pt will not melt until you get to 1768.3 °C so I think that would put |P.G.M's in a very specialist assay bracket as it will need alloying to bring the melt temperature down or a very high-temperature furnace with specialist flux's as the boiling point of regular flux's such as Borax is only 1,575 °C.
Quite a large subject to expect intimate instruction on, a very interesting subject of inquiry nun the less.
Only very expensive thermocouples can operate at such temperatures so I just go by the old blacksmith's adage, red is low heat white is high heat.


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## Topher_osAUrus (May 30, 2017)

Losses due to volatization with gold and silver occur well under the boiling point of the metals. I want to say it starts (minimally) around 1150 or so, and gets significantly worse the higher you go. I do believe this is dependant upon many other things as well, such as the base metals in the melt mix, and the flux being used, as well as the amount of "current" (draft) in the furnace.

I will have to look it up again to know definitely, but, Im pretty sure those numbers are quite close


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## solarsmith (Jun 1, 2017)

Thermocouple has arived ( a few hrs ago) and I drilled a hole in a fire brick and am suspending the end of the thermocouple even with the top of the cupel about 1/2 inch away. I am watching the glow at the top edge of the cupel and at the end of the thermocouple folow each other very closely. I have three ways to control the temp. 
1--- opening the gap in the fire brick on top 
2--- the gas valve (propane)
3--- placing a air valve on the intake of the shop vac.

I am able to get over 1000 C in just a few min.


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## Eu_citzen (Jun 20, 2017)

solarsmith said:


> can any one tell me what temps I should use for a gold silver platinum cupel? I just did a cupel in a propane furnace and my lazer temp device was maxing out at 950 f even the out side was reading in the high 800s f. thanks Bryan



Depends on the collector you use.

I think I use around 700 Celsius for lead, going up slightly near the end to remove all lead. 
(been using bismuth exclusively lately - so take it with a grain of salt)
Bismuth requires a higher temp; around 850-900 Celsius.

Building an electric furnace is quite easy, I'm in the process of repairing a damaged heating element in my "DIY" furnace. I'd grab some pics next week. (holidays, first!)

The basics are:
Fireproof brick
heating element (I use Kanthal)
PID temp. controller
Thermocouple

Then you may need some iron to put it all together and some insulation.


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## Eu_citzen (Jun 26, 2017)

Solarsmith, check the "work in progress" in the DIY section. I put up some pics of my furnace there.


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## rhwhite67 (Jul 10, 2017)

Piece of strong advice from someone who wast taught assaying by the best assayer in Colorado who ritered years ago and shared his secrets. DON'T Cupel EVER!!!. He was putting platinum group assays in peoples hands back in the 60's when PGMs weren't supposed to exist in the US. If you look in a assay oven during cupelling you will see little sparks like fireworks going off your lead button. That is your PGM's sparking / flying off. Also I know of a guy who used to go around to various mines in Nevada and collect their old used cupels. He was making really good money crushing and leaching the Au and Ag that got sucked into the cupels by poor cupeling procedures. 

Take that lovely lead bead you have and clean it thoroughly to remove all of the slag. Smash that guy plat as you can or run it through a jewelers rolling mill to flatten it. Cut it into pieces and dissolve it in 5-10% Nitric and distilled water solution. Filter, dry the powder, and weigh it this will contain your Au and PGMs minus the Pd.

Your lead, copper, Ag, and Pd will be in the Nitric. If you look in the Forum yo will find methods to separate these. Then weigh the separate powders recovered. Use standard chemical processes as listed in the forum to separate you Au from the Pt, Rh etc PGMs.

In doing so you will have a true assay of the recoverable metal in your ore. 

Also follow ALL safety protocals in dealing with acids etc!!!!!! They can be a valuable tool but they can also be very nasty if not used properly. 

Good luck on your endeavors.
Ron


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## Topher_osAUrus (Jul 10, 2017)

rhwhite67 said:


> ...He was putting platinum group assays in peoples hands back in the 60's when PGMs weren't supposed to exist in the US.
> Ron



....What?
You mean 1860s?..


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## Eu_citzen (Jul 10, 2017)

I think if you're seeing sparks off your lead button, something's wrong.


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