It's convenient to think in 4 broad categories:
Naturally colored diamonds, mined from the Earth, cut and
polished with no additional treatment.
Naturally mined diamonds, often of "poor" (faint yellow or brown)
color, but subjected to irradiation to create a host of other
colors, from pastel through vivid. Most common are yellowish greens,
yellows from pastels through golden orange, steely colored blues and
Naturally mined diamonds of a certain crystal type which are pale
yellow/brown but through the HPHT (high pressure-high temperature)
process can be relieved of their coloration to yield D-E-F colors
worth substantially more. SUBSTANTIALLY more! This treatment can be
very difficult to detect
Diamonds grown in the lab using HPHT modified processes.
Colorless is hard and expensive to produce, not really profitable.
Yellows through oranges are the most commonly seen, but greens,
blues, pinks and reds are produced as well. Separation from natural
can be easy or very difficult.
That should raise questions without end, and I would strongly
recommend a search of the literature for more info; GIA is a good
place to start....
As far as business practices go, disclosure is mandatory. Some here
say they wouldn't sell them, but, IMO, their snobbery is affecting
their bank account adversely. I will and do sell synthetics and
treated goods to jewelers and end users, and will eventually happily
sell to the folks that some will not sell to because they won't
carry the goods. Sorry, I'm in business to sell things, I let the
market and my clients determine what to buy, not my pre-conceived
notions of what is "good". The FACT is that there is a growing market
among the "new" consumer for "bling". I didn't create that market,
but I profitably cater to it. I didn't create hair dye, either, but
Revlon seems to be doing okay with their brand of deception.
Gemesis just ordered 100 new HPHT machines to manufacture
diamond....somebody's buying it. And if you turn away those
customers, they will find someone who WILL sell to them. If that
someone is ME, I guarantee that you have lost that customer forever.
So my only advice here would be to learn about these products so
that you can knowledgeably and ethically offer them to your clients,
with disclosure, of course. What THEY tell their friends is THEIR
business (see Revlon).
And I cannot keep diffusion treated synthetic (!) blue sapphire in
stock. The jewelers I sell to enjoy strong markups from it and it is
beautiful and provides a less expensive than the natural. Women get
it, men don't, need I say more?