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Couple questions


#1

Hello all, I have been searching for the answers to a couple
questions but can’t seem to find answers. I would appreciate it
if you could point me in the right direction if you don’t have
the answer.

  1. I was given several gallons of Hydrochloric and Nitric acids.
    I was going to make Aqua Regia then make the dilution’s for
    testing the different carat weights of gold. I can’t seem to
    find any info on the dilution’s for 10, 14, 18,24ct testing
    solutions. And what about Silver testing with it?

  2. I know Aqua Aura is made by putting a layer of gold over
    Quartz crystal. It can only be a micron or two thick, and I know
    it can’t be done by electroplating. Any suggestions?

Thank you in advance,
Larry Beezhold- Durnings Rings & Things

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#2

Larry, I suspect that this info is already in the archives, but
here is what I do. I keep 2 small glass stoppered bottles. I have
etched an “N” on one and an “H” on the other. I keep nitric acid
in one and hydrochloric acid in the other. In addition I have a
black touchstone and samples of varying karats. I will rub the
unknown on the touchstome until I get a decent gold mark. Then I
will rub a sample of the suspected karat next to it. Perhaps
another sample on the other side. I will then drop a single drop
of nitric acid on the rubbings. Ten karat or less will blacken
or turn green. Higher karats will generally show little or no
reaction. Enter the hydrochloric acid. A single drop added to the
nitric on the unknown and samples will now produce a reaction.
The sample that most closely matches my unknown will will be the
corresponding karat. Some other possible tests. File a notch in
the unknown. Add a drop of nitric acid. Green foam indicates
base metal. Cream colored foam suggests sterling and black may
indicate coin silver.

    2) I know Aqua Aura is made by putting a layer of gold
over Quartz crystal. It can only be a micron or two thick, and
I know it can't be done by electroplating. Any suggestions? 

That’s a good question. My understanding is that this is a vapor
deposition. I wish that someone would complete the
explanation.

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#3

G’day Larry; One uses aqua regia at full strength for all carat
weight alloys - as far as I know. To test for alloys one
streaks the gold on a piece of slate, then streaks beside the
mark a series of thin gold pieces of known carat strength, and
compares the colours, then adds nitric acid and compares the
colours again. There are more accurate methods these days, but
they all need very expensive equipment.

 And what about Silver testing with it? 

Aqa regia won’t dissolve silver. You see, as soon as the nitric
acid reacts to produce a silver compound, the chloride ion in
hydrochloric acid will convert it to silver chloride, which is
quite insoluble, so the reaction stops at once. You can dissolve
silver in concentrated nitric acid (it dissolves easily with
brown fumes of nitric oxide - poisonous). Add a drop of
hydrochloric acid or a solution of table salt (sodium chloride)
and you will get a white precipitate which turns a grey-violet in
sunlight. To prove you really have silver there, add ammonia to
the solution containing the precipitate and when you have added
enough to neutralize the acid, the solution will become clear.
(it will get hot too) If you add an excess of ammonia, you will
get a pale blue colour due to copper if you began with sterling. >

2) I know Aqua Aura is made by putting a layer of gold

over > Quartz crystal. It can only be a micron or two thick,
and I know > it can’t be done by electroplating. Any
suggestions? > The gold colouring you seem to be thinking of is
done by evaporating pure gold on to the quartz in a high vacuum.
Because it would soon rub off, the gold then has a thin coat of
pure silica evaporated onto it in the same way. Doing this needs
lots of expensive equipment. (I built and used apparatus for that
in 1948 when I was employed by a research association in
Sheffield. With vacuum evaporation one may coat almost any
object with a metal of choice.) Cheers, – John Burgess;
@John_Burgess2 of Mapua Nelson NZ

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#4

Hello Larry,

Lucky you!!! It’s hard here in Germany to get a hold on
Hydrochloric- and Nitric acid.You got to have a licence or
anoter justification in order to buy them. Anyway,I’ve got some
for you but only for the first question !!

concentration for 333 kt gold: 2 parts nitric acid to 3 parts
water (distilled water)

concentration for 585 kt gold: pure concentrated nitric acid.

concentration for 750 kt gold: add a little amount of
hydrochloric acid to the concentrated nitric acid.

concetration for silver: 1 part of nitric acid to 3 parts of
hydrochloric acid (agua regia). This solution creates a white
deposite of silverchloride which turn into a dark violet color
depending on the amount of silver in your metalstrike used by a
touchstone procedure.If the metal doesn’t contain any silver,the
metalstrike stay’s gray or dissapears after a while.

I’m sure that people have other recipes but this is what I know
using the chemicals you mentioned in your e-mail.

Be carefull and use a well ventilated room.Add acid to water
(slowly!!)and not the other way around.Add acids together slowly
and check out the reaction.Work in a area where you can easely
provide yourself with clear water in case someting happends.have
somebody (adult!!)as a backup if something should happen to you
and brief the person in case of.Definetly keep it out of reach
for children. If,however,something should happen,prepare next
solutions before you start working with the chemicals.Make a
mixture of calcium and water to drink or a lot of milk if some
of the acid mixture is swallowed by accident.In addition swallow
chrunced ice cubes after drinking the milk and contact a doctor
as soon as possible.Do not try to vomit since this causes double
trouble.Wash off immediatly spilled acid on your skin with clear
cold water and alcalic soap.Wear eye goggles and gloves even if
you’re shure that you’re save and chose good ones.Don’t
drink,eat or smoke during the procedure.If you work inside take
the person immediatly outside to breath fresh air.After you
completed your work,take the time to wash yourself befor you
eat,drink,smoke or shake hands with someone. It all sounds a
little bit tomuch,but believe me I have seen it and it wasn’t
plesant to see and I’m not a softy.Precautions are saving your
and other peoples live.

Regards Pedro
Palonso@t-online.de

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#5
   That's a good question. My understanding is that this is a
vapor deposition. I wish that someone would complete the   
explanation. 

It IS vapor deposition. The first part of the explanation is
the note that this is industrial level processing. Don’t expect
to be able to do this yourself, unless you’ve got some really
substantial engineering background to make the equipment. But
there are firms that will do such coating for you.

As to how it’s done, first imagine the old vacuum tubes used in
pre-transistor radios. Remember how they were always blackend
around the electrodes after being used for a while? What happens
is that under a vacuum, the heater filiment, which is also under
a high voltage in order to send an electron stream towards the
various anodes/cathodes of the tube itself, is also sending a
stream of it’s own atoms, propelled by that voltage. The stop
when they hit the glass, and form that black deposit. In a
vacuum tube, this eventually results in the tube burning out. In
vapor deposition, it’s harnessed. Here, in a high vacuum
chamber, a metal electrode (whatever you wish to deposit) is
heated high enough so that under a high voltage, some metal
evaporates, and the ions are projected towards the other
electrode by the voltage. In a way, its sort of like
electroplating, except there is no bath dissolving metal ions,
only heat evaporating them, and a voltage propelling them. When
they hit whatever is in the way of them, they deposit. It’s a
line of sight process, the atoms don’t turn corners, so complex
shapes may need several electrodes spaced around the chamber in
order for all surfaces to be covered. Multiple electrodes can
also be of differing metals simultaneously, with differing
voltages applied to each, in order to coat an object with a
complex coating, like an alloy, except that the process isn’t
limited to just metals. Anything that can be vaporized and
ionized can be coated this way. Those gold colored burrs coated
with titanium nitride? I’m pretty sure those are vapor
deposition coated. Buy a plastic hobby shop model of a car and
some of the plastic is chrome plated for the bumpers? Those too
are often vapor deposits on the plastic. The coatings can be
VERY precisely controlled too, for thickness. In electron
microscope use, non-conductive objects being viewed (like organic
things) must be vapor deposit coated with gold, in order for the
sample to be viewed. Since you can then still see all parts of
the object even under very high magnification, you can imagine
just how thin and precise those gold coatings are in order to
not obscure the details of the item being imaged… In optics,
vapor deposition is often the method used to make things like
multilayer interference filters, and sometimes, lens coatings.
All in all, a rather useful technology. And while, as I said,
it’s out of the reach of most artists, not all. I have seen
some folks using this technology to coat objects, such as things
being then imbedded in acrylic castings, for example. While I
suspect that those pieces were coated by a commercial firm for
the artist, you could, if you’ve access to a high vacuum pump and
suitable experience in high voltage power supplies, build such an
apparatus. just be aware that this is NOT the sort of vacuum
pump we use for investing. I really do mean HIGH vacuum.
Expensive pumps. And the voltages involved aren’t exactly easy
and safe to play around with either. Not quite a radio shack
spare parts piece of equipment to cobble together.

Hope this helps.
Peter Rowe


#6

And what about Silver testing with it?

You can dissolve

silver in concentrated nitric acid (it dissolves easily with
brown fumes of nitric oxide - poisonous).  Add a drop of
hydrochloric acid or a solution of table salt (sodium chloride)
and you will get a white precipitate which turns a grey-violet in
sunlight. To prove you really have silver there, add ammonia to
the solution containing the precipitate and when you have added
enough to neutralize the acid, the solution will become clear.
(it will get hot too)   If you add an excess of ammonia, you will
get a pale blue colour due to copper if you began with sterling. 

Is this the basis of “Schwarter’s (sp?) solution”? I have heard of
Schwarter’s solution, but have never been able to find any,
especially locally. I would really like to find what is in
Schwarter’s solution. I am told that in years past, Schwarter’s
could be purchased in chrystalline form, and desolved in water for
use. Does anyone know anything about Schwarter’s?