I've got a question for specialists in bullions, or for smart chemists :
A friend of mine went to sell a gold coin (a perfectly good Maple Leaf) at a big jewelry store. Unfortunately the jeweller turned out to be a crook.
So the crooked jeweler says, "I'm going to test the coin for its gold composition. I'll drop a small drop of acid on the coin, on its border/brim... But first, look, to begin with, let's try dropping acid onto this pure square of gold that I have here with me, and, see, the acid does nothing"
(the crook drops acid or whatever on a small golden square thing, and there's no reaction.)
The crook resumes : "Good, now I'll drop my acid on your coin. It should produce no reaction if it's gold indeed."
(acid or whatever it is, is dropped onto the gold coin, at the border/brim, and startlingly, after a few bubbles subside, the border of the coin turns a very bright silver color, as if gold had disappeared to reveal silver underneath).
At this stage the crook says " Oh too bad, it's silver coated in gold, almost worthless". He then puts an oily brown liquid on the silver-coloured stain, "to stop the acid from eroding further the metal".
As a result, the gold coin (which is 100% authentic, by the way, it was proven later on by other means) is now stained, with a dark brown cloud over the gold, at the spot where the chemical products were applied.
So my question is, what was the chemical used to produce this bubbling, then the bright silver color onto the gold coin, and what other product was used later on to turn the "silver stain" into dark brown? Also, how to wash it. My friend washed it with white vinegar and the stain faded but far from totally disappeared.
Was this chemical reaction(s) due to the fact that the gold Maple Leaf has a very, very small percentage of some alloy in it (zinc or copper?) to make it less malleable?
I'm thinking now, was all this, Aqua Regia being poured onto a small part of the gold coin?
How close of a friend is this? Do you have a pic of the coin? I know a reasonable bit about gold and this story sounds like there must be more to it.
To what end would the crooks game be? To simply ruin people's otherwise good coins? Most people upon simply being told their $2000 coin is worthless, won't just say "ho hum, might as well leave it with you then". They'll probably get a second opinion, discover it's still an oz of gold, and although you might not get the price you would for a pristine coin, a "slightly damaged" oz of gold, is not worth much less than a
near mint" oz of gold. Chemistry, and the chemistry of gold specifically(alchemists of middle ages are probably responsible for way more than their share of chemical discoveries), was one of the most studied fields of the last thousand years. It's very unlikely some 2 bit thieves are discovering new chemical reactions of gold, particularly with a simple on top of the shelf apparati, and garden-variety level chemicals. Additionally, specialist chemicals have specialist prices, often many x the price of gold.
Gold generally does not react with acids, specifically nitric acid(it's used to test it), so wouldn't be that as Road2Damascus said. There's a specific mixture 3:1 nitric/hydrochloric if I recall, they will dissolve it called agua regia, or "king's water". It was supposedly used to hide gold in the middle ages. "Don't mind those random bottles of liquid while your raping and pillaging".
Mercury will dissolve gold, but that's a purely physical process. And it is pure metallic mercury, not a dissolved compound. That was one way of refining gold in the old days. Dissolve it, since rock and other impurities won't, make bricks of gold amalgam, transport, boil off the mercury, try not to inhale the fumes, profit?
.9999 gold is actually very good. Today's "gold standard" as it were. It only became wide spread maybe 25 years ago, previous being .999. It's not .9999 gold, and .0001 zinc or like that, it's .0001 other, by virtue of technical limits of separation and refining.
Think of it like this. You grab a 5g bucket of stony swamp muck. You can pull out big rocks and sticks by hand go from 30% water to 60%. Run it over a screen made of sticks to get rid of small gravels. up to maybe 80% Through a basic cloth to get rid of sands. Now you have probably 96% pure water. You're probably around the limit of what you can do on site. To go further, you need specialized filter papers to remove the dirt. But now there's maybe 1% salt. You can get a very small, very high cost membrane, like they use for desalination on sailboats, with holes on the atom size level, apply high pressure and get rid of the salt. Now you're probably around 99.99, but even still there will be dissolved gasses (o2) from the air, other dissolved solid in the ppm range (look at the back of a bottled water label). The point being, it's 10 times more work to get from .999 to .9999 as it is to .99 to .999, which is probably 50,000 x as hard as goin from .00001% pure (sitting in a river bed in a sea of rocks) to 90% pure (pluck out the nugget).
Finally, if this were any kind of common wide spread scam, you'd most likely of heard about it. If someone rips off a dozen people selling TV boxes filled with sandbags in a parking lot of a medium sized city you hear about it on the news. And again, to what gain would this be?