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Rhodium blackened diamonds


#1

Hi all.

Here is a curly one. The other day I sized a ring (brand new) for a
shop and after doing this several of the diamonds went black (or
very dark). Now I have been a jeweller for a long time and I have
never seen this before. It has since happened several more times but
never with my own jewellery. The rings are clean and it is not cooked
dirt. It doesn’t seem to do all of the diamonds, just the odd one. I
replaced my cleaning solution and cleaned the anode in it.

I am using a platinised titanium anode in the rhod sol. What the ??

Thanks.
Darren.
Ace of Diamonds Jewellery

[edit] Attachment removed [/edit]


#2

Hello,

A goldsmith I set stones for once experience that very same problem
of diamonds getting really dark after some modification involving
soldering was done to a brand new piece of jewellery. That particular
piece happened to be of Chinese origin.

There is an odd “treatment” done on yellowish diamonds, in which a
bluish fluoride coating is applied to the pavillion, making the stone
appear whiter, and if the diamond is set on a closed type of setting
is really difficult to notice. Who knows, maybe the stones that went
so dark after heat had their pavillions coated that way, and what
happened is that the “paint” burned over the surface of the diamond.
Bottom line, no matter what he did to that piece, he couldn’t solve
the problem, and that triggered a huge quarrel with the retailer: a
years long work relationship broken by or over a suspicious chinese
earring.

Fernando


#3

What normally colours diamonds, eg yellow to red?

If these are non-bonded pigmentation minerals then the stone is
properly called a rock and not a mineral. It is not a pure mineral
gem.

So that broadens the discussion to impurities in diamonds. What does
one call these impurities? Inclusions? Alloy-of-diamond? I’m lost
for words.


#4

Hello,

After making a brand new 18ct white gold ring with a silver/palladium
alloy, the same thing happened…There were about fifty pave set
diamonds in the ring and four of them turned a deep yellow/brown when
the ring had been completed and rhodium plated. When I investigated
further, I remembered that I had had trouble with the drill-bit on
occasion and in one area the bit had broken in the hole I was
drilling… the colouring of the diamonds corrisponded with the areas
that the drill-bit had stuck/broken. Is it possible that the rhodium
reacted with the steel (even though I removed all of it???) and
coated the diamonds? Incidently, placing the entire ring into a
strong acid bath sorted it out an the colouring did not happen the
second time it was plated…

Maybe this might shed some light?
Gwen


#5
What normally colours diamonds, eg yellow to red? 

Peter, colored diamonds generally owe their color either to
structural defects in the lattice, or to various impurities included
in the crystal. The most common is atoms of nitrogen, which can occur
in a number of structural varieties, giving rise to most of the
yellow, brown, or canary tones. Boron is responsible for some of the
blue and blue/grey colors (and also makes these types uniquely
electrically conductive). Damage to the crystal lattice, such as
from radiation, can give you greens, and somewhat related structural
defects due to plastic deformation of the crystal lattice gives you
the pinks and reds.

Wikipedia has a decent entry on diamond color, and for more detail,
I’d start with Kurt Nassau’s “Gemstone enhancement”, which also gives
references for even more detailed discussions on diamond color

If these are non-bonded pigmentation minerals then the stone is
properly called a rock and not a mineral. It is not a pure mineral
gem. 

Not sure what you’re dreaming about here. Color in diamond is
intrinsic to the structure or flaws in the structure of the material,
or to atomic level inclusions taken up within the crysta structurel.
It’s not pigments, for heavens sake… And diamond is a mineral, not
a rock. Rocks are mixes of more than one type of different minerals,
with the rock being an aggregate or mix of the different types of
crystals. This does not describe diamonds, though you could apply it
to the raw mined source rock, such as Kimberlite, from which the
diamond crystals are separated out.

So that broadens the discussion to impurities in diamonds. What
does one call these impurities? Inclusions? Alloy-of-diamond? I'm
lost for words. 

Lost for words. Hmm. No, I think you got it the first time.
Impurities and inclusions about covers it. But inclusions don’t
account for most color in diamonds. Atomic level impurities or
structural defects without other elements gives you the colored
diamonds. Inclusions, as with any other crystals, refers simply to
whatever stuff got accidentally taken up and trapped by the growing
crystal. In diamonds, the most common inclusions are other diamond
crystals. Often, the so-called “carbon” black inclusions in some
diamonds are simply other diamond crystals that appear black. But you
can also get other minerals included in diamond. Garnets are not
uncommon, for example. Usually these don’t materially affect the
diamond’s color. In these respects, diamond is quite like a number of
other gem materials. When pure, it’s colorless. So is quartz, so it
Topaz, and so is Corundum (sapphire). In all these, the inclusion of
other elements taken up into the crystal structure as impurities, or
the occurance of crystal defects in the structure of the crystal,
allows these minerals to occur in a variety of colors. Diamonds, even
colored diamonds, are mineral, not rock. Same thing with Citrine or
Amethyst quartz, various types and colors of Topaz, ruby, emerald,
aquamarine, sapphire, etc.

The real words you might be looking for are allochromatic and
idiochromatic. these are distinctions between minerals who owe a
color to an essential element always found as part of the chemical
formula that defines the mineral.

Idochromatic minerals are not clear white when pure, but are always,
if that mineral, the defined color, deriving the color from an
essential componant of the mineral’s chemical makeup. Examples are
malachite, (whose color is from copper), Olivene (iron), almandite,
rhodochrosite, and many others.

Allochromatic minerals/gems owe their color to impurities or
variable types and degrees of crystal lattice damage or
irregulatiries. All of these can vary. Thus beryl can be colored
light blue (aqua) or bright green (emerald) or other colors depending
on variable impurities. Same with tourmaline, sapphire/ruby,
diamond, topaz, quartz, and many more.

Hope that helps
Peter Rowe


#6

A corollary to this question/comment has to do with how much of
these pigmentation mineral impurites might be included without
breaking the C bonds when diamonds are made synthetically?


#7

Thank you for the free educational material.

I discovered some intense blues and greens in my prospecting; so
intense I first though they were paint and then I thought they might
be due to living creatures like microbes or even rock inhabiting
lichens.

I am reading the book “Colour” by Hong Kong journalist Victoria
Finlay (South China Morning Post) who went on a world tour to learn
the history of pigmentations, ie paints. Much of her layman’s
findings pertain to minerals.

If diamond contains an alien mineral is it not then a rock rather
than a mineral by definition? Does the word carbonatite apply to the
rock?

Is it more correct to call coloured diamonds, carbonatite?

Mineral pigments in diamond could, from a layman’s perspective, be
due to microscopic cracks which fill with mineral pigments suspended
or dissolved in water. This might be called sedimentary. Later
intense heating of the diamond stones might then have an effect on
the colour and/or bonding of pigment to host stone. Metamorphic?

Does anyone here make synthetic diamonds in their garage? Does
anyone here sell the machinery to make diamonds? What kind of prices
are we looking at?

How would one add mineral pigments to the magma so as to bond the
pigments inside the diamonds (igneous action)?

I’ll see if I can get Nassau’s book.

BTW, would even the De Beers lab at the University of Alberta know
if a rogue prospector had “salted” a deposit in the tar sands region
of Northern Alberta with diamonds made in his garage? They are
prospecting in blue clay are they not?

Not that I would do this but my sidekick, Penelope Dirtbag might do
the deed.

Meanwhile back on planet Earth I am also learning about colouring
dimension stones. Acid baths have striking effects on some of the
stones I am using for my backyard stone garden and not others. The
resulting colouration looks natural (paint does not). Does anybody
else use chemicals to colour field/dimension stones like this? I am
looking into something I googled across called “soil cement” as I
have a pond which I am lining with stones and mortar to keep the
water in and I don’t want to use plastic. Does anyone know about soil
cement?

Piper the Prospector


#8
If diamond contains an alien mineral is it not then a rock rather
than a mineral by definition? Does the word carbonatite apply to
the rock? 

If you had a material that was clearly defined as a mix of diamonds
with other minerals as a mix of the different crystals, then that
would be a rock. I’m not aware of any such, but that doesn’t mean it
couldn’t exist. The name of such a rock could be whatever the
geologist describing it wishes to name it. Granite, for example, is
a name that clearly describes a certain class of rock, but which
gives no clue to the seperate mineral types that mix to make up a
granite. But be careful. Simply having a few diamonds imbedded in
something doesn’t make that “something” a different material. Shale
with dramatic crystals of garnet imbedded in it makes wonderful
specimins, but it’s still a shale, abeit one with nice garnet
octahedra imbedded in it. And accidental inclusions of some other
mineral inclusions within a diamond crystal doesn’t change the
identity of the diamond. It just makes it a diamond with certain
inclusions, which might, if they are interesting or significant, be
themselves identified.

Is it more correct to call coloured diamonds, carbonatite? 

“Earth to Peter”… Are you listening? Did you read what I wrote the
last time? I’m beginning to wonder why I bother responding to your
posts since you clearly are on your own trip, and not actually paying
attention to given you unless it agrees with what you’ve
already decided you want to be true. Maybe that’s unfair, but I’m
beginning to suspect…

Anyway. No. Colored diamonds are diamonds. And by the way, the
impurities that give colored diamonds their color are NOT pigments,
and don’t function the way pigments do. Pigments are minerals that,
as particles or grains of significant size, are able to reflect or
absorb certain wavelengths of light all on their own. The pure
pigment powder has a color because of this. Mixed into a binder, or
imbedded in another material, they still function on their own,
optically distinct from the host material. So pigment mixed with
linseed oil gives you a paint the color of the pigment. Nitrogen, on
the other hand, is colorless. If it worked as a pigment, it’s
presence as a trace impurity in diamond would do nothing. Instead,
it gives us yellows. And as has also be noted, many colored diamonds
do not owe their color to an impurity at all, but rather to damage,
defects or dislocations in the lattice structure. As with the
occasional replacement of a carbon atom with a nitrogen one, this
affects the way the overall structure affects light. It’s not the
nitrogen by itself. It’s what the nitrogen or other impurity does to
the way the whole crystal-- carbon, impurity, and the resulting
structure-- does to light and absorption spectra.

Please stop trying to invent new descriptions of why colored
diamonds are colored. The structures and mechanisms of these things
are already quite well known. You don’t need to imagine new and
wonderful names and mechanisms, just read up on what’s already been
described. Reinventing the wheel doesn’t work so well if your apple
cart sports a brand new wheel that is square, and has the axle
mounted in one corner. Well, I’ll restate that. Keep on doing it if
you like. But you’re wasting your (and our) time.

Mineral pigments in diamond could, from a layman's perspective, be
due to microscopic cracks which fill with mineral pigments
suspended or dissolved in water. This might be called sedimentary. 

This does, actually, rarely occur. Usually gives reddish dirt
coloring to the cracks. Doesn’t color the whole diamond. Not
generally a good or desireable effect, but can be interesting in an
academic sort of way. Not called sedimentary, since sedimentary
deposits are actual sediment, such as silt or sand settling out from
a body of water. Traces of a mineral being carried into a crack is
generally just called a stain…

Later intense heating of the diamond stones might then have an
effect on the colour and/or bonding of pigment to host stone.
Metamorphic? 

No. Just a burned diamond. Geez, dude… Relax, will ya?

Does anyone here make synthetic diamonds in their garage? Does
anyone here sell the machinery to make diamonds? What kind of
prices are we looking at? 

Depends on what you call a “Garage” Chatham has a building in which
they make diamonds. So does Gemysis (spelling?) and so do others. But
the custom built machines used for this are themselves about the size
of a small car. And they aren’t cheap. Generally need a whole lot
more electricity than is available in the normal residential
garage… I doubt you can just find a catalog to buy the things. But
if you root around enough in the right industries over in Russia, you
might always find someone with such surplus equipment (where these
things were first made for actual commercial production) I’d guess
these things cost somewhere between a few hundred thousand to a few
million each. Just a very rough guess… Oh, and did I mention, THEN
you have to figure out how to actually make diamonds with the things.
Not as easy as just having the machines…

How would one add mineral pigments to the magma so as to bond the
pigments inside the diamonds (igneous action)? 

Holy Crap, dude. You want to add mineral pigments to MAGMA? (Not
lava. That occurs at the surface with volcanic eruptions, but
diamonds don’t form in it there. Magma is a lot deeper. ) Ok. Here
goes. First hitch a ride on Jules Verne’s expedition to the center of
the earth, or any of those several bad Science Fiction films that
purport to be traveling into volcanos or otherwise in the general
direction of magma. When you figure that part out, get back to me and
we’ll figure out your damn pigment. Remember that if you want to be
affecting color in diamonds, you’re gonna need to get around a
hundred miles down, well below the crust, and into the upper mantle
of the earth.

Oh, and did I mention too, diamond color isn’t due to pigments?
yeah, I think so. As to adding anything, that part’s easy. In the
case of nitrogen in diamond, for example, the reason that synthetic
diamond production is mostly yellow colors is that it’s really hard
NOT to get nitrogen into the stones, given the fact that synthesis is
being done here on the earth surface, where we have this atmosphere
thingy that’s mostly nitrogen. The stuff is everywhere. No doubt bad
for you. Try not to breath too much of it. Prolly causes cancer or
something. Other impurities, well, again, if the atoms of the
appropriate other impurities are floating around in the same stuff
where the diamonds are growing, then they’ll be incorporated
automatically. They’re not added after the crystals are grown.

I'll see if I can get Nassau's book. 

PLEASE DO. And a few others too, while you’re at it. The need is
obvious.

BTW, would even the De Beers lab at the University of Alberta know
if a rogue prospector had "salted" a deposit in the tar sands
region of Northern Alberta with diamonds made in his garage? They
are prospecting in blue clay are they not? 

Hey, if you’re gonna be salting deposits with your hard grown
synthetics, would ya let me know? Please salt my back yard, while
you’re at it, so I don’t have to go so far. Thanks.

Oh, and yes, DeBeers or GIA or others could tell the difference.
Synthetic diamonds, like many other gems both synthetic or natural,
leave trace clues to their origin. Not always easy, but so far, they
can tell the difference. Not to mention that usually, if they find
diamonds where the geology doesn’t strongly suggest that there SHOULD
be diamonds, then they’re more than likely to be bright enough to
take a good hard look… And tar sands have a VERY different
geologic history than sediments or primary deposits likely to have
diamonds.

Not that I would do this but my sidekick, Penelope Dirtbag might
do the deed. 

Naughty girl. But save her the potential legal hassles of a hoax or
fraud. Like I said, I volunteer my back yard, or better, the floor on
my workshop under my workbench, as a great place to toss your
synthetic diamonds. I’m often down there already, looking for genuine
diamonds I’ve dropped, so your salted diamonds are much more likely
to be discovered. I can make an appointment for you or her to come
over and perform this salting at any time you wish. I await your
call. If the line is busy, please don’t hang up. I’m probably talking
to that fellow from Nigeria that has all those millions of dollars he
wants to give me 'cause he knows he can trust me and all. Still
working on that angle, but when it pans out, I’ll help you as an
investor in the cost of your diamond growing machine…

Peter Rowe
(and please, don’t confuse me with the Peter I’m replying too. We’re
VERY different people, I suspect…)


#9

Some comments on observations put forth by Piper the Prospector:

If diamond contains an alien mineral is it not then a rock rather
than a mineral by definition? Does the word carbonatite apply to
the rock? 

Well, no. Any mineral mass or crystal could contain an inclusion.
The inclusion does not mean that the crystal is a “rock.” A diamond
"rock" would be something like lots of little diamonds cemented
together with olivine and garnet crystals. Or maybe a “sandstone” in
which the sand is all diamond. Nothing of the sort has been observed
on earth, of course, so this is entirely imaginary.

A carbonatite is a rock, true enough, but it is made up of mostly
carbonates. Carbonates are salts of carbonic acid, a weak acid formed
when carbon dioxide gas dissolves in water. Common carbonates
include limestone, dolomite, siderite, and mixtures of these. There
could be diamonds formed in the upper mantle when carbonates are
subducted and their chemistry altered by the melting that takes
place at that zone. That is conjectural. Perhaps entire coal seams
have been subducted at some point in earth’s history. That would
place a lot of concentrated carbon in the correct
pressure/temperature domain to form diamond.

Is it more correct to call coloured diamonds, carbonatite? 

No, not at all correct, for reasons enumerated above. Diamonds are
pure carbon, except for minor inclusions in some of them. They are
not carbonates.

Mineral pigments in diamond could, from a layman's perspective, be
due to microscopic cracks which fill with mineral pigments
suspended or dissolved in water. This might be called sedimentary.
Later intense heating of the diamond stones might then have an
effect on the colour and/or bonding of pigment to host stone.
Metamorphic? 

One would not expect to find mineral “pigments” within a diamond.
Diamonds are formed in the mantle zone of the earth, many kilometers
below the surface and far below “sedimentary” rocks. Diamonds have in
fact been mined from sedimentary beds in Brazil, but these are
secondary deposits, maybe even tertiary deposits, since no-one knows
where they were originally formed. Diamonds are sometimes associated
with an honest-to-goodness metamorphic rock known as eclogite.
Eclogites rarely come to the surface since they are made miles and
miles down in the upper mantle. It takes a fluke of tectonic plate
movements to bring a bit to the surface where we can see it.
(California has a couple of spots, one on the Tiburon peninsula,
another near San Jose.) Eclogites might be the end result of
metamorphisms of a rock that began as a simple silt at the bottom of
the primitive ocean a few billion years ago.

Does anyone here make synthetic diamonds in their garage? Does
anyone here sell the machinery to make diamonds? What kind of
prices are we looking at? 

Making synthetic diamonds is a major industrial process, most
unlikely to be done in a garage. Companies making diamonds also
create their own machines and closely held processes. Don’t expect to
find either machinery or processes for sale, at any price.

How would one add mineral pigments to the magma so as to bond the
pigments inside the diamonds (igneous action)? 

Magmas are totally inaccessible to human intervention. The closest
any human can approach a magma is when a volcanologist on the Big
Island samples the outflow from one of Kilauea’s vents. So don’t
plan on adding anything to a magma.

By the way, diamonds aren’t found in just any old magma It has to be
a kimberlite or lamproite.

If you ever got close enough to a magma to identify diamonds within,
just wait for the magma to cool and mine the diamonds. No need to
fool with them. And diamonds crystallize best without any
impurities, whether you want to call them pigments or something else.
So there are no pigments within a diamond.

It takes far more than “igneous action” to affect diamonds anyway.
They form at narrow conditions of pressure and temperature. If
conditions are not right, the stable form of carbon is graphite, not
diamond. We’re talking 50 - 60 kilometers below the surface. There
is a lot of info available on the subject available on the Internet
if you want to pursue the details. That problem also means that
diamonds have to be transported from their original high pressure
home to the low pressure on the surface of the earth in a very short
time, which implies very high velocity expulsion of kimberlite
peridotite up the tube from that magma chamber miles down.

I'll see if I can get Nassau's book. 
BTW, would even the De Beers lab at the University of Alberta know
if a rogue prospector had "salted" a deposit in the tar sands
region of Northern Alberta with diamonds made in his garage? They
are prospecting in blue clay are they not? 

If a rogue prospector has succeeded in making diamonds in his
garage, he could probably make his fortune by selling his new and
cheap method to one of the commercial outfits making synthetic
diamonds so they wouldn’t have to spend millions for it the way they
do now.

By the way, tar sands are sedimentary, and any “blue clay” that
might be associated with the sands is most assuredly not the
unweathered kimberlite known as blue ground, a solidified peridotite
within a diatreme or pipe leading from a subsurface magma chamber to
the surface. And yes, a De Beers lab would probably know, since one
of the difficult things about synthesizing diamond is doing it
without nitrogen contaminating the crystal and turning the result
yellow or brown. A garage diamond maker would probably have extreme
difficulty making a nitro-gen free diamond, or any diamond at all,
for that matter!

My remarks are for educational purposes.

Richard Davies


#10

Blackening of Diamonds after De-Stoning process in Aqua Regia

August 1, 2018
Q. Dear Sir’s
I introduce myself as Prakash V Pai from India.
I work as a senior manager, Castings in a firm which manufactures Gold & Studded jewelry for Exports.
Our Exports consists of 75-80 Studded jewelry. Recently one of the orders were cancelled by a customer who had ordered studded rose gold rings. The cancellation was done when the cast pieces were in QC stage. Due to this, we rejected the entire production.
To de-stone the jewelry and to recover the gold, I had to process the rings in Aqua Regia acid which we normally do without any problems, but this time the stones changed color and turned from white to blackish.
image|583x500
I tried boiling the stones in order to recover the original color by doing the following process:

  1. Re-boiled the diamonds in Aqua Regia.
  2. Boiling the diamonds in Perchloric Acid
  3. Kept the Diamonds in Cyanide solution
  4. Boiled the diamonds in Hydrochloric Acid
    All the above processes did not yield any results and the diamonds had a shade of black with it.
    Can somebody please explain and shed some light, as to what was the cause of diamond turning black?
    How to clean it again to bring back its original whiteness? What are the chemicals I need to use?
    Re Cutting & Re Polishing on lathe again of diamonds means loss … Please Help!!
    Eagerly awaiting for your reply…
    Warm Regards,

#11

These stones had, most probably, been coated in order to improve their color. The acid treatment seems to have either removed or changed that coating.


#12

Hi Tony…
Nice to hear from you…
After several acid processes & without results, I had my doubts on the same.& could not confirm the same due to lack of knowledge.
I have few questions which come to my mind at this moment…

  1. Can you Please shed some light on this process of Coating diamonds…
  2. What type of Chemicals are used for coating diamonds ( have heard of Blue Fluoride Powder).
  3. How do I differentiate from Normal Untreated Diamonds & the treated Diamonds??
  4. Is there any way we can reverse this blackening??

Awaiting for your reply,
Warm Regards,
Prakash V Pai
INDIA…


#13

Alas… this is all beyond my knowledge!

Tony Konrath

tonykonrath@mac.com


#14

Thanks Tony… that’s Ok…
Regards
Prakash V Pai