Best melt technique for small batches

So I’ve run through about 10 experiments recovering gold from computer parts and some karat jewelry as well as some G filled material. I have right around 18 g of powdered gold, which seems quite pure when dissolving in AR.

I’m just looking for what you guys think might be the best way to melt this down… I have regular propane, and map gas torch...kaowool, ceramic dish, and borax. In the mix there are going to be at least two filter papers, according to the pH of solutions they filtered, they should not contain any chloride ions.

From all the different things I’ve read and seen, it doesn’t seem like you can overdo it on the borax or sodium carbonate because Au doesn’t dissolve in those liquefied materials. But I’ve been wondering if I should go ahead and make the jump to a electric furnace so that I don’t lose anything for sure from torch blow, considering I have quite a bit of precious metals already (to a newb) Convincing the wife notwithstanding, just wondering what you gentlemen do

With purer gold no need for fluxing.
I never had a need for a furnace to melt refined gold.

Heat your dish slowly to dry out moisture before bringing the temperature up on the dish, sprinkle borax in your dish like you are salting your food, the goal is to only give a glass glaze of borates to the ceramic dish.

Not much need for a furnace environment if your torch can produce enough heat, and you do not lose that heat through convection (dish setting on concrete sucking heat as fast as your torch can produce it0.

With the glazed ceramic dish sitting on a pad of ceramic wool (asbestos pad) or something that reflects heat and does not suck it up, and your gold in a dry glazed melting dish, we can heat the dish bringing it up to a glowing red heat, do not focus the torch on the powder blowing it out of the dish, circle the dish only slightly lapping some flame and thus heat over the top of the gold, focusing on circling and heating the dish mainly.

let the gold powder begin to fuse before bringing the torches focus onto the gold, then use the torch to further melt and even shove or force the molten gold around with the torch in the red hot dish, to pick up the small beads to form one molten button.

Mapp gas is plenty hot enough, but much depends on your torch, (as well as maintaining that heat) some torch heads are hotter than others, a good torch head cost a little more but are a good investment, not advertising but I have had a good result using a TS8000 made by Bern zomatic.

Not necessary, but to help keep me from blowing out gold or paper, before I learned how to use the torch better on fine powder, I would dampen the paper and gold with alcohol lighting it off to burn the paper, crushing the ash before torching the dish, the alcohol can help to keep the gold in the dish a while if you get a little too wild with your torch on the powder before it has a chance to fuse or begin melting.

My choice normally is acetylene/oxygen or with a change of tips and gas propane and oxygen, the torches get hotter have different torch heads, and these are just good all-around tools, for melting gold, cutting or welding, again these cost a little more but can pay more for themselves in the end.

Thanks for the detailed response, definitely will try the alcohol trick where are you speaking about ethanol or isopropanol. I had such a difficult time melting my first batch of cement silver and I figured out that it was because of the concrete slapping all the heat out of my melt dish, so I’ve been real nervous about trying it on my gold.

The alcohol either kind will work, if used, the idea is to initially wet the gold with a flammable material that will do no harm or add anything, but can be helpful to burn the paper to carbon and thus ash, and help wet the gold powder to initially help hold it together helping to keep the powder in the dish from the force of your torch.

Wrapping your gold in a small ball of toilet paper, then wetting it with a drop of alcohol will also help those not used to using a torch on fine gold powders.


After gaining a little practice with your torch you will have no need for alcohol.


A trick I often use when I dry my gold powder, the way I do it makes tight balls of tightly packed gold powder, In a small beaker on a coffee cup warmer (mini electric hot plate) I wash my gold, when drying before completely dry (a thick mud with little water none visible).
I hold by the rim of the beaker with one hand and bump the bottom of the small beaker on the heel of the other hand.
This forces all the gold powder to bang against the side of the glass, driving out water, circling the beaker, and continuing banging, and the gold will form a tightly packed mud like a ball, or balls. which can be put under a forceful torch with no worries of blowing powdered gold out of the dish, which can be helpful if melting gold with a rosebud torch.
.

butcher said:

The alcohol either kind will work, if used, the idea is to initially wet the gold with a flammable material that will do no harm or add anything, but can be helpful to burn the paper to carbon and thus ash, and help wet the gold powder to initially help hold it together helping to keep the powder in the dish from the force of your torch.

Wrapping your gold in a small ball of toilet paper, then wetting it with a drop of alcohol will also help those not used to using a torch on fine gold powders.

After gaining a little practice with your torch you will have no need for alcohol,

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Can I do Silver the same way?

I do not see why not, it would be better than blowing it out of your dish.
Note: I edited my post above to add content, to discuss a trick of how I make gold balls, instead of starting another post.

I melt my gold by pouring it in wet into the dish then drying it in the dish in the oven. this make it hard and nothing ever blows out. when you first put the torch on it do it for a second or two and take it away if still damp you will see the steam. do that a few times and when it goes dark to light its dry.

This works for me and always have. I find drying it them pouring it into a melting dish as a good way to lose gold. I've even dried it in the dish wet with a torch. this work best on small amounts of gold under 6g. You can precipitate and melt within 15 minutes.

Eric

Alabama938 said:

Thanks for the detailed response, definitely will try the alcohol trick where are you speaking about ethanol or isopropanol. I had such a difficult time melting my first batch of cement silver and I figured out that it was because of the concrete slapping all the heat out of my melt dish, so I’ve been real nervous about trying it on my gold.

Click to expand...

What part of Bama are you located in sir?

Currently in PA, from Gadsden, went to Bama, Roll Tide

So I tried butchers technique, I probably didn’t do it all the way correctly, I couldn’t seem to get the entire mass of gold to liquefy instead it just solidified down to a chunk with sharp edges that never seem to move, I was using the MAPP gas torch, let it run for almost 30 minutes right on the gold after it shrunk down, maybe 2 cm away from the tip of the torch maybe 3.

It’s not pretty but it’s the coolest freaking thing I’ve made, probably ever, I just want it to be round and smoother

It has nice color.

You can either apply more heat, usually by upgrading to a more expensive type of torch, or you can try to keep the heat you're currently producing from escaping. Try to create a condition around your melting dish that keeps heat from escaping.

Dave

Alabama938 said:

Currently in PA, from Gadsden, went to Bama, Roll Tide

So I tried butchers technique, I probably didn’t do it all the way correctly, I couldn’t seem to get the entire mass of gold to liquefy instead it just solidified down to a chunk with sharp edges that never seem to move, I was using the MAPP gas torch, let it run for almost 30 minutes right on the gold after it shrunk down, maybe 2 cm away from the tip of the torch maybe 3.

It’s not pretty but it’s the coolest freaking thing I’ve made, probably ever, I just want it to be round and smoother

Click to expand...

WOW! Roll Tide!
PM me!

That gold is just absolutely beautiful.

What in the heck does the fire of our torch have to do with the chemistry of metals or moving electrons?
what part of my torch is hotter?
How can I better understand what my torch or burner does to my metal or to a salt of my metal?

I cannot explain this well in typing or writing, how can I do it better?

Different parts of the flame coming from your torch tip or furnace burner will have different properties.

Oxidation (lose of electrons)
Reduction (Gain of electrons)
Oxidizing (ability to take electrons)
Reducing (ability to give electrons)

Many torches or burners can be tuned or adjusted, adjusting an oxidizer fuel ratio, and thus these different properties. Normally propane or a Mapp-gas torch are normally tuned in their construction of fuel/air ratio and non adjustable, and will hold that tuning as long as the torch head is clean and not mechanically damaged (from corrosion or other).

The yellow portion of the flame is cold in comparison, just in front of the very tip of a blue cone is the hottest part of the flame.
the yellow flame is a reducing agent for metals, If the torch is sooty and smokey it is also producing another reducing agent, carbon, to the mix.

The blue cone of the torches flame has an excess of air or oxygen, an oxidizing flame, also meaning it can take electrons from metals that are fairly easy to oxidize or metals which are more reactive. this portion of the flame can oxidize a metal (take iron for example making a salt of that metal or rust, iron oxides or take electron from copper to form copper oxides.

Gold is not very reactive at all even in most melts, gold cannot be easily oxidized, chloride salts are one flux that can oxidize gold in a molten state.
Just as excess oxygen in a melt can more easily take electrons from a more reactive metal in a melt to form metal oxides, and just as carbon can reduce metal ions in a melt converting say copper oxide to copper metal.

In welding we often use flux to help offset this oxidation process of our torch or welding environment, basically controlling the oxidation reduction of the welding environment to give us a good bond or bead (which may also be formed as different allow of the two metals we are bonding or the welded area may even have a different crystalline structure, but this can also be somewhat from the alloying but more from the heating and cooling process of the metal which is a factor of forming the crystal structure of the metal the bead or even the metal around the weld that we have changed the crystal structure of in our welding process.
Such as of smaller more densely packed crystal structure and thus a harder metal structure but more brittle and easier to break, or of the softer larger crystals more loosely packed that help the metal bend or be more malleable or easy to bend or stretch easy.

I did not want to get into welding but if we do a little it can give us a better idea of what is going on.

Gold will also have a crystal structure ( not considering alloying here), and this structure can be changed mechanically by working the gold, rolling, hammering bending...(gold or copper are also different than iron in how the metal is hardened or softened or how we change the crystal structure of the different metals).

Gold can be hardened under a hammer, or by bending, as you smash the metal or bend the joint you are changing the crystal structure making it harder more brittle easier to crack under more work, harder to stretch of change its form.
We can rearrange or change the crystals to make the gold soft again by heating it to red hot in a re-crystallization process as we get the gold atoms excited or moving around. Pure gold can be dipped in water for cooling and further annealing, while other alloys of gold (like with nickle) cooling may be done differently such as cooling slower on a cool metal plate, Nick being a jeweler will know more about how gold alloys react to heat treatment, my skill is more in the field of blacksmith so I understand iron better than gold.

The yellow portion of the flame is lower in oxygen, richer in fuel, and thus a reducing flame, or saying it another way, it can give electrons to metal oxides or salts of metals, as the oxide ion portion of the metal/oxide ionic compound and carbon (from burning of the fuel burn) (to produce carbon monoxide, water and excess carbon), basically, the black smoke (incomplete combustion) where even the excess carbon in the exhaust gases of your torch can become a flus to help produce a chemical reaction, the flames smoke can act as a flux or a reducing agent in a melt of metals again giving electrons to the metals ions.

As the metal oxide or salt can be reduced to molten metal or as the metal ions gain electrons to form metal atoms or an elemental metal, For example in a reducing environment we can change copper oxide (a salt of copper) to copper metal.

An oxidizing flame or environment can take electrons from the copper atoms, making a salt of copper or copper oxide out of our copper metals.

A reducing flame or environment can give electrons or convert copper oxides to copper metal in a melting process


An oxidizing flame, Blue flame (note the word I used), this oxidizing flame also refers to metals being melted or welded in a fusion process of two metal pieces and where we often alloy metal in our forming a welded bead in the joining two metals, and we also often use a chemical flux to clean or oxidize metal in the process (take electrons), or preform other chemical changes (or move those electrons)(as well as using our torch's oxidation or reduction properties) our flux may also have reduction properties or ability to provide electrons, so just as our torch or burner produces chemical change so does the flux or chemicals added to the melt.

I tried to proof read this several times with my bad eyesight and failing ability to write, I hope this is readable and makes some sense to you.

Thanks for the responses, I like the info on melting flames and environments, that’s why I thought a blue inner cone, 2cm from the tip would get me there, but ima have to add oxygen I think to truly control a melt and be able to manipulate the small amounts, I’ll be getting in these small recovery batches.

I like the idea of holding more heat in, I was thinking about a small forge with kaowool, so many variables to consider.

What a great hobby thanks again guys for all the advice

If you can make a small 3 sided enclosure around your melt dish and line it with kaowool that should help retain the heat in your dish, hearth firebricks will do or better still soft firebricks which do not need lining.

The physics of melting is basically easy. If you add heat from a flame and loose heat to the environment the melt will have it's temperature somewhere between the flame and the surrounding environment. If you have a problem reaching melting temperature then you could either bring in more heat from a hotter flame or a bigger flame. Or isolate the melting dish to better conserve the heat.

A simple way is to put the melting dish on a ceramic blanket to isolate the bottom or make a small cavity that reflects the heat back to the melting dish. The ultimate cavity / reflector is a furnace with insulation on most sides.

I struggled a lot with an lpg torch but when I arranged a few fire bricks into a small cavern it was easy to melt my gold.



Lately I've switched to an acetylene torch as it is just so much faster.

Göran

So I used an oxy-propane torch, using the little red bottles. I melted the previous chuck together with a few more small chunks from another few runs. Now it’s 26g, but the oxygen ran out after maybe seven minutes, is this common these little red bottles running out so fast, did I run too much oxygen?

I follow the instructions of the OP torch inserts, I had another regular MAP torch aimed at the crucible sitting stagnant. The 0P torch had a 2 cm blue cone. I had no idea the oxygen run run out so fast, this might be an expensive torch to use, I might invest in a small electric furnace versus making a small propane furnace because that oxygen usage just doesn’t seem cost effective

One has to admit learning to melt is almost as as much as a challenge as recovery but practice in this case makes perfect 8)

I would have to agree… I have some academic experience with chemistry so I felt like that part came pretty easy, but the Melting has really got me frustrated

Yes, those small red bottles run out really fast. When using one to weld with it lasts about 5 to 6 minutes, and around that when melting high temp metals.

How long will map-pro gas yellow tank last?