There sure is a lot of information out there on man made diamonds!
First, the basics about diamonds. They're made of strongly bonded
carbon atoms, and 'in the wild' they're formed under very high
pressure over many thousands of years.
A common myth is that a scientist called Tracy Hall made the first
artificial diamonds, but this urban legends site gives us the true
"A team in Sweden made the first artificial diamonds on Feburary 16,
1953. They subjected graphite to 83,000 atmospheres and unspecified
heat generated by a thermite shell (barium peroxide & magnesium). They
repeated their work on May 24 & Nov 25, and had the Nov 25 diamonds
verified by an independent diamond expert. Strangely, they made no
announcement until 1955, after the GE team's announcement, and
provided no process details until Lundberg published a 1960
retrospective, so nobody had a chance to duplicate their efforts. They
only produced a fraction of a carat of tiny diamonds, and their secret
efforts to perfect the process were scooped by GE's public
announcement in 1955, so they abandoned the project (well, actually,
they sold out to deBeers). As a result of these misjudgements, they
get no credit for the discovery but are "relegated ... to little more
than a historical footnote."
At GE, a six-man team worked on the project for several years. GE's
Herb Strong thought he had made diamonds on Dec 8-9, 1954. He started
with carbon powder, iron foil & seed crystals, cooking them overnight
at 50,000 atm and 1250 deg C (with some mysterious temperature
excursions due to a faulty controller). The team found 2 crystals of
dubious origin (could've been the seed crystals) embedded in the iron
foil. One of the other team members said that they then "wasted weeks"
trying unsuccessfully to repeat the experiment.
Only a week after Strong's run, GE's Tracy Hall made diamonds on Dec
16, 1954. He started with graphite, iron sulfide & seed crystals, but
he needn't have bothered with the seed crystals. Cooking his sample at
100,000 atm, 1600 deg C for only 38 minutes, in a press different in
design from Strong's, he made a mass of tiny diamonds. The experiment
was successfully repeated by Hall and by independent GE researchers --
and by Percy Bridgman, who'd been trying unsuccessfully for years to
make diamonds at Harvard. GE patented Hall's process, the Dept. of
Commerce slapped a secrecy order on it, and so although they could
announce the discovery in 1955, they couldn't disclose any details.
Hazen suspects that the GE team had made diamonds before then, but
hadn't really known what to look for. The GE samples that would
confirm this have been lost through carelessness, and so the world
will never know."
This site: http://www.pbs.org/wgbh/nova/transcripts/2703diamond.html
deals with the creation of large (big enough for jewelry, not tennis
ball size) diamonds in laboratories, and how this might impact upon
the jewelry industry, and whether graphite (also made of carbon) can
be turned into diamonds. One of the experts interviewed is none other
than Tracy Hall! It makes for interesting reading and answers your
question, but I won't post the whole text here, it's too long!
Some interesting out-takes:
"ALEX GRIZENKO: A diamond is a diamond. If it's carbon and if it looks
like a diamond, it's a diamond. It's not a simulant. And as we know,
there are many simulants on the market. Cubic zirconia has been around
for many years. A new simulant called moissanite has entered the
marketplace. But these are all pretending to be carbon. They're not
carbon. Hence, they're not diamonds."
"NARRATOR: It was the evidence the GE scientists were looking for.
They hoped that a metal called troilite, when heated into a liquid,
would act as a solvent to break the bonds between the carbon atoms in
graphite - and do it at a pressure and temperature that was lower than
the levels they had been using. They tried adding some troilite to the
H. TRACY HALL, SR.: It was a wintry day, it was cold but the sun was
shining through the window, and I had put some troilite in this
graphite tube, I put it in my belt apparatus. I turned up my heating
system and I put the pressure on.
ARCHIVE FILM NARRATOR: The force builds up and up and up, eventually
reaching nearly 500 tons, almost one million pounds per square inch.
The outer surfaces reach 750 degrees Fahrenheit, inside 2600 degrees
NARRATOR: They hoped that the carbon atoms in the graphite would
dissolve into the molten troilite, and then when they had reached a
high enough temperature and pressure, would crystallize as diamond.
HERBERT STRONG: We were in the hunch stage - my hunch was that, when
you're in the diamonds pressure region and you melt the metal, and
these carbon atoms dissolve, then it turns out the metal says hey,
I've got too much carbon in me here, I'm going to have to precipitate
it out some way to get rid of it, and the way to do that is to
precipitate it out in the form of diamond.
NARRATOR: They could only risk running their machine at full pressure
for a few minutes. But they had no idea whether this would be enough
for diamonds to form. Just as they had done dozens of times in the
past five years, they broke open the capsule.
H. TRACY HALL, SR.: So I got down to the point where I picked things
apart and got to look at what there's in the middle, and my eyes
caught the gleam of the sun shining on these things, and I, you know,
twirled it around a little bit and saw the sparkles, and at that
instant I knew that man had finally turned graphite into diamond. My
knees weakened, I had to sit down, I was overwhelmed."
"Today, nearly 90% of all diamonds used in industry are manufactured.
But these tiny crystals would never be gems. GE was able to grow
larger diamonds in the 1970s, but they cost more to produce than the
price of natural diamonds. For the time being, the market in large,
gem quality stones is dominated by a single player. De Beers is the
diamond business, and controls the world diamond trade from this
building in the heart of London. Over four billion dollars' worth of
rough diamonds are sold here every year. An equal amount is kept on
reserve. One of the ways De Beers has managed to keep the market value
of diamonds high is by stockpiling some of its inventory. Many of the
world's diamonds comes from DeBeers' own mines in Africa. But DeBeers
has also formed strong partnerships with many other mining companies
around the world. And when new sources of diamonds are discovered - in
places like Siberia and most recently in Canada - De Beers moves in.
Their goal is to protect the value of diamonds by controlling their
release. It's impossible to know how much time and money is spent in
search of diamonds, but it's clear that the amount of effort it takes
to produce even a single engagement ring is impressive. It is
estimated that for every one of these rough stones, 250 tons of rock
must be mined and processed. By weight, that's a ratio of more than a
billion to one"
I hope this has answered your question! If you need clarification,
feel free to ask.