How to buy a diamond?

Hello everyone,

This must be a very frequent question and please forgive me if I’m
being too redundant. A friend of mine has asked me to design and
fabricate his engagement ring. Platinum with a princess cut diamond.
I mostly work in silver sometimes in gold and am very eager to get my
feet wet with platinum, but am little scared as to where to start.
I’ve been reading up on stuff, and will continue. I live in NYC so my
questions are:

What are some places I can buy diamonds from, I know of Diadeb, but
haven’t gotten in touch with them, a friend of mine suggested Leo
Wollman, but I know they’re better for colored stones. What is the
process of buying a diamond, are there certificates involved, or?What
should I know, I mean I know the grading systems, however I don’t
know how to apply that when lookign at a diamon? IS there a place
where I can find out a going price for diamonds. Also, if anyone
knows a good stone setter, a friend of mine suggested someone but
they’re not taking any more customers. I would love to talk to them
and see how I need to prep the setting for them to be able to set the
stone. I’m sure I have more questions, but if anyone can point me in
a good direction I would really appreciate it.

Thanks,
Mia