Understanding reactions (gold processing, and Identification)

[CattMurry]

Hello friends. I had a broad range of different questions that I hoped to be answered where the experts lie. So, my first question would be gold plated materials versus polished brass.

I am seeing some use 14k gold testing acid (nitric I assume) to test metals, but it reacts strait through any gold plated material as well. Would the 10k acid solution do the same thing thus being too strong?

I was thinking, and know that HCL did a little magic for me testing audio jacks that I could not determine the composition of. The HCL attacked a few pieces with what I suspect zinc was in while leaving others untouched, and keeping their shine. The shiny pieces I assumed then were gold, or plated with AU.

Now my confusion with my results. I have some very tacky looking jewelry that I wanted to test, but I wanted to firstly test my brass method once more. Some of the brass I kept in solution, then some pieces like a door handle guard I dipped into HCL then let open to the air. I then proceeded to speed the reaction up with a heat gun for the material open to air. It appears that the polished brass resists the HCL, but the HCL finds imperfections in the material to penetrate into. The issue would be that this would look the exact same for gold plated materials with underlying metals. Why does the polished brass resist the chemical reaction so well?

I also was wondering on the reaction of HCL with zinc to form zinc chloride. Is there a way to precipitate the ZnCL2 back into it's oxide form to then smelt with coke?
All corrections, and answers are greatly appreciated. I am no chemist haha.

 

[butcher]

Plated and karat gold are two different animals, I wouldn't test or treat them in the same manner.

You need to do some study to learn the different tests we can use, it sounds like you are jumbling different types of tests or processes together and do not understand any of them.

Nitric is used with karat gold, scratching the metal on a stone leaves a marked trace of the alloy on the stone, a drop of nitric will dissolve the base metals from the trace, leaving the remaining gold in the streak with another streak made on the stone with the known carat gold testing needles, to make a comparison if both streaks the known and the questioned metal being tested are compared are the same they have the same amount of gold or are of the same karat if you were testing brass that mark would dissolve, where your known gold karat mark would still have undissolved gold...

Scratching the surface of the metal and a drop of nitric can reveal if the item is plated then some HCl can determine if silver is involved...

Different combinations of water, nitric, and HCl, (differing strengths of aqua regia) are used to make different strengths of karat gold testing solutions, like 10k 14k... The more concentrated the solution used for the higher karat gold, the weaker solution is used for nongold or low karat gold testing (normally used with stone and scratch comparison tests), but it can be used as drops on a scratch in the ring or metal itself in some instances...

Yes, you could spend your time learning how to use electrolysis to get the metal from solution, or learn to chemically convert the zinc into an oxide, and learn how to smelt it, but why spend a bunch of time trouble, and money on something that would cost you far more than what you made was worth.

Do a search (here on the forum for Hoke's books she has two books, one of her books was dedicated to testing precious metals, also do a search for Pawn Broker's guide to testing precious metals, one or both of these books are great for your library, and a study will get you back on track in understanding what you have with these metals.

 

[CattMurry]

Plated and karat gold are two different animals, I wouldn't test or treat them in the same manner.

You need to do some study to learn the different tests we can use, it sounds like you are jumbling different types of tests or processes together and do not understand any of them.

Nitric is used with karat gold, scratching the metal on a stone leaves a marked trace of the alloy on the stone, a drop of nitric will dissolve the base metals from the trace, leaving the remaining gold in the streak with another streak made on the stone with the known carat gold testing needles, to make a comparison if both streaks the known and the questioned metal being tested are compared are the same they have the same amount of gold or are of the same karat if you were testing brass that mark would dissolve, where your known gold karat mark would still have undissolved gold...

Scratching the surface of the metal and a drop of nitric can reveal if the item is plated then some HCl can determine if silver is involved...

Different combinations of water, nitric, and HCl, (differing strengths of aqua regia) are used to make different strengths of karat gold testing solutions, like 10k 14k... The more concentrated the solution used for the higher karat gold, the weaker solution is used for nongold or low karat gold testing (normally used with stone and scratch comparison tests), but it can be used as drops on a scratch in the ring or metal itself in some instances...

Yes, you could spend your time learning how to use electrolysis to get the metal from solution, or learn to chemically convert the zinc into an oxide, and learn how to smelt it, but why spend a bunch of time trouble, and money on something that would cost you far more than what you made was worth.

Do a search (here on the forum for Hoke's books she has two books, one of her books was dedicated to testing precious metals, also do a search for Pawn Broker's guide to testing precious metals, one or both of these books are great for your library, and a study will get you back on track in understanding what you have with these metals.

I am familiar with the aqua regia (royal water). It is able to put gold into solution, while nitric will react to base metals, and silver. My main confusion would be brass, and specifically gold plated material. I have seen through the youtuber Streetips that the 14k solution will in fact eat strait through/around the gold plating if it is plated AU to get to the base metals. It does that through imperfections I'd imagine. I'd like a method to determine what is brass, and what has gold plating, because both reactions with nitric will be too similar. This is where I have tested HCL to attack the brass, and more specifically the zinc. Brass will tarnish into a dull copper looking material with HCL applied, but I am seeing that polished brass is having resistance (the door handle guard example). I am confused how it is resisting the HCL reaction. Moreover this will confuse my test results with gold plated materials. I am basically also asking how people even determine their materials are gold plated versus brass/brass plated/or even gold painted to begin with. Even streetips said he did not know which is unusual to hear. Thanks for the answer(s) friend.

 

[FrugalRefiner]

Brass will tarnish into a dull copper looking material with HCL applied, but I am seeing that polished brass is having resistance (the door handle guard example). I am confused how it is resisting the HCL reaction.

Many decorative brass items are coated with a clear layer like various types of paints (lacquer, acrylic, enamel, etc.) to protect the metal from tarnishing. Without the protective coating, the items will tarnish and become brown instead of the attractive polished brass color. Have you removed any possible coatings from your door handle guard?

Dave

 

[CattMurry]

Many decorative brass items are coated with a clear layer like various types of paints (lacquer, acrylic, enamel, etc.) to protect the metal from tarnishing. Without the protective coating, the items will tarnish and become brown instead of the attractive polished brass color. Have you removed any possible coatings from your door handle guard?

Dave

THIS is what I thought too, but when putting a flame to it for a good minute nothing happens.... I was impressed to say the least. I also was wondering about paints reaction with HCL, and it appears that HCL in general (I Use the baume 20 degree 31.5%) will eat at paints vigorously, but that is only what I have read. Good suggestion friend. Maybe the clear coat is rather heat resistant? I did not use a torch.

 

[FrugalRefiner]

Hit it with a file, a scraper, sandpaper, etc., then try again.

Dave

 

[CattMurry]

Hit it with a file, a scraper, sandpaper, etc., then try again.

Dave

got a file set, so will do. It already eats the backside of the trim (what I called the handle guard), so I am aware it works, but I guess I am more confused on why HCL won't eat the shiny surface even if it is paint. Thanks for the replies Dave!

 

[FrugalRefiner]

Well, there are paints, and then there are paints. When I was young (the dark ages), there were basically enamel and lacquer paints. Now, "paints" can include epoxies, plastics, and plenty of other clear coatings. Their purpose is to prevent corrosion by any variety of environmental chemicals, so, in essence, they've been developed to resist all the acidic components of our modern atmosphere.

Even in Hoke's time, her advice was to file a deep notch, then test.

Dave

 

[CattMurry]

Well, there are paints, and then there are paints. When I was young (the dark ages), there were basically enamel and lacquer paints. Now, "paints" can include epoxies, plastics, and plenty of other clear coatings. Their purpose is to prevent corrosion by any variety of environmental chemicals, so, in essence, they've been developed to resist all the acidic components of our modern atmosphere.

Even in Hoke's time, her advice was to file a deep notch, then test.

Dave

Yeah... I attempted to compare, and see mixtures of paints used, and woah. You aren't wrong about the plastics that really do a great job preventing acid bleed throughs. Great advice Dave!

So in essence my gold test for gold plate versus brass is valid unless paints are used. Scary. I'll stick to computer scrap, and Karat gold lmao. Inquarting sounds way more fun than these testing regiments although for computer scrap the HCL is very handy.

Wanted to ask if there was a way to drop zinc from HCL. Does the zinc turn to it's chloride form? (ZnCl2) Finding it hard to find if it can be cemented out. Just curious as to I enjoy learning this chemistry.

 

[Elemental]

A short story:

Some kind soul gave me the ground plates out of an old building. These are copper plates about 1/2 inch in thickness, 6 x 10 inches in size. I decided to use one to try and cement some silver and nothing happened. Pulled it out, gave it a rinse and a dry and then hit it with a pocket torch. Sure enough, a clear coat that I had missed started to melt and pool on the copper. It got thrown back on the shelf until I can figure out if it's worth dealing with.

Elemental

 

[CattMurry]

A short story:

Some kind soul gave me the ground plates out of an old building. These are copper plates about 1/2 inch in thickness, 6 x 10 inches in size. I decided to use one to try and cement some silver and nothing happened. Pulled it out, gave it a rinse and a dry and then hit it with a pocket torch. Sure enough, a clear coat that I had missed started to melt and pool on the copper. It got thrown back on the shelf until I can figure out if it's worth dealing with.

Elemental

Paints man. Very sly stuff. Good info. all! Could you not just burn it off with the exception of the horrific fumes? lol

 

[FrugalRefiner]

Yeah... I attempted to compare, and see mixtures of paints used, and woah. You aren't wrong about the plastics that really do a great job preventing acid bleed throughs. Great advice Dave!

It's really not fair to call them paints. If you look at the information here about "solder mask", you'll find that one size does not fit all. Different manufacturers create different coatings depending on their requirements balanced against costs and many other considerations. They can require quite different processes.

So in essence my gold test for gold plate versus brass is valid unless paints are used. Scary. I'll stick to computer scrap, and Karat gold lmao. Inquarting sounds way more fun than these testing regiments although for computer scrap the HCL is very handy.

A strong hard drive magnet will detect gold plate.

Wanted to ask if there was a way to drop zinc from HCL. Does the zinc turn to it's chloride form? (ZnCl2) Finding it hard to find if it can be cemented out. Just curious as to I enjoy learning this chemistry.

Most folks here don't try to recover most base metals. Copper is useful, but refining is additional work. I've never tried to recover zinc.

Dave

 

[Elemental]

Paints man. Very sly stuff. Good info. all! Could you not just burn it off with the exception of the horrific fumes? lol

I could burn it off (would probably sand it off though to make sure it's all removed), but being that I don't know what it is, or what's in it, I doubt I'll use it for refining. Life is just easier when you keep the chemistry clean. As Dave pointed out, base metals are treated more like consumables. I use new copper grounding wire for cementing out precious metals and plain iron/steel bars for waste treatment. I could recover the copper sponge and re-melt it, cast it and use it again, but since I'm using a cheap tabletop furnace with graphite crucibles, I've found I'll spend more on crucibles than I likely would on recovering that copper. It wasn't too long ago someone was trying to give away several 55 gallon barrels of copper sponge, without much luck. Turns out the metal recycling center wasn't interested in it, while it was in that form.

Elemental

 

[CattMurry]

I could burn it off (would probably sand it off though to make sure it's all removed), but being that I don't know what it is, or what's in it, I doubt I'll use it for refining. Life is just easier when you keep the chemistry clean. As Dave pointed out, base metals are treated more like consumables. I use new copper grounding wire for cementing out precious metals and plain iron/steel bars for waste treatment. I could recover the copper sponge and re-melt it, cast it and use it again, but since I'm using a cheap tabletop furnace with graphite crucibles, I've found I'll spend more on crucibles than I likely would on recovering that copper. It wasn't too long ago someone was trying to give away several 55 gallon barrels of copper sponge, without much luck. Turns out the metal recycling center wasn't interested in it, while it was in that form.

Elemental

Good points. For some reason sanding/grinding went right over my head. Clean chemistry is definitely best.

 

[CattMurry]

It's really not fair to call them paints. If you look at the information here about "solder mask", you'll find that one size does not fit all. Different manufacturers create different coatings depending on their requirements balanced against costs and many other considerations. They can require quite different processes.



Most folks here don't try to recover most base metals. Copper is useful, but refining is additional work. I've never tried to recover zinc.

Dave

Oh sorry for the confusion. I literally meant that first part for all paints that could possibly be used in/on jewelry, brass, and nearly everything else. By paint I also am meaning to say coatings as well. Solder mask looks interesting. I believe I have seen it here, and there on mobos. Seemed almost like a ceramic in a way. Any tips for running into that? I just chiseled it away haha.

"A strong hard drive magnet will detect gold plate."
Now this.... what's this my friend? How does this work? I am quite intrigued.

Zinc is just really reactive, so I didn't know if there was a simple way to have it quickly go into the HCL then drop it back out.

I should add that my main goal in all of this is to find a suitable solution with HCL, and bleach/hypochlorite/Chlorine/Sodium chlorate methods to refine with, because like many other's on the forum have stated.... I could live happily with chlorine with it's ability to be filtered with corresponding..... well filters.

 

[olawlor]

"A strong hard drive magnet will detect gold plate."
Now this.... what's this my friend? How does this work? I am quite intrigued.

There's normally a nickel barrier or strike layer under a gold plating. Nickel is strongly ferromagnetic, so even a micron layer shows some attraction to a magnet. Gold and common alloying metals like silver, copper, etc are very weakly diamagnetic, so won't stick to a magnet at all.

 

[butcher]

A strong magnet can detect a nickel plating under a gold plate.

More reactive metals can be harder to recover, take aluminum for example at one time it was worth more than gold, as it was harder to make from ore, although aluminum ore is not rare and extremely common. Today aluminum is cheap it like other metals in elemental form can be more easily recycled, but not easy to mine and convert to metal from ore or in ionic form, Hard for large companies even harder to do in a backyard with a budget you do not have to waste.

A study of dealing with waste would be helpful in your question of precipitating zinc as well as other metals from a solution, using pH or forming hydroxides or using sulfides...

Study how salts of metals can be converted to oxides with high heat and oxygen or air driving off the acidic salt ions as gases (roasting), (scorification), and the metal oxidizes in the red heat.

Study displacing a metal from solution using a metal that is more reactive (reactive series of metals).

We can convert one salt of metal into a different salt of that metal like converting a metal chloride to a metal sulfate...

A study of electrolysis of zinc...

 

[Jado]

Also of note… Certain brass and bronze alloys are highly resistant to HcL and were commonly used for distilling it before 316SS and the new carbon composites existed

 

[CattMurry]

A strong magnet can detect a nickel plating under a gold plate.

More reactive metals can be harder to recover, take aluminum for example at one time it was worth more than gold, as it was harder to make from ore, although aluminum ore is not rare and extremely common. Today aluminum is cheap it like other metals in elemental form can be more easily recycled, but not easy to mine and convert to metal from ore or in ionic form, Hard for large companies even harder to do in a backyard with a budget you do not have to waste.

A study of dealing with waste would be helpful in your question of precipitating zinc as well as other metals from a solution, using pH or forming hydroxides or using sulfides...

Study how salts of metals can be converted to oxides with high heat and oxygen or air driving off the acidic salt ions as gases (roasting), (scorification), and the metal oxidizes in the red heat.

Study displacing a metal from solution using a metal that is more reactive (reactive series of metals).

We can convert one salt of metal into a different salt of that metal like converting a metal chloride to a metal sulfate...

A study of electrolysis of zinc...

No kidding there my friend. I do need to deep dive into balances, reactivities in mixed solutions, and getting everything to it's oxide forms from the salts. Thanks for the tips my friend. Helps to know where to start.

 

[CattMurry]

It's really not fair to call them paints. If you look at the information here about "solder mask", you'll find that one size does not fit all. Different manufacturers create different coatings depending on their requirements balanced against costs and many other considerations. They can require quite different processes.

A strong hard drive magnet will detect gold plate.

Most folks here don't try to recover most base metals. Copper is useful, but refining is additional work. I've never tried to recover zinc.

Dave

Wanted to return to confirm it was clear coat on that brass (handle guard), or trim as they say. I left it in the HCL and a day later expected for it to turn to jelly, and it in fact turned to jelly. From that I can test what has clear coat applied. Heating will probably quicken the reaction, but may also make a mess with the paints if too hot. Good original call Dave.