Diamonds without a certificate of origin these days may be 'blood diamond=
s'.

Is a "blood diamond" a diamond that DeBeers didn't get a cut of the
profit on? Is it a diamond that was used to fund a rebellion that the
UN didn't approve of? Is the UN's approval really that excellent a
marker of "legitimacy" of uprising? Is the UN going to put a ban on
Iraqi "blood oil" sold under American (USA) auspices; "we'll fund the
war by selling the oil we grab there." Is a "blood diamond" a way
somebody can make a living in a ravaged country without having to kill
other people? Doesn't all the talk about "conflict-free,"
"transparency," "certification" sound suspiciously like big government
and busy-body hippies poking their clueless fingers where they don't
belong and or they will do some third party the most good?

I don't know. I do know that what I read about "blood diamonds" and
the quickness "oooo, don't buy blood diamonds" gets mentioned sure
makes me think it sounds like a load of propogandistic hooey.

Point? If you are going to take William's advice and avoid _POSSIBLY_
buying a "blood diamond," have a look into it and try to really
understand the issue for yourself before you mindlessly buy into some
other person's boycott. Boycotts are trendy and so often misguided.
This one may well be too. And when they are, they do tremendous harm.

Pass them through an international border (by post or in your pocket) you
stand a chance of getting them impounded.

Now that's a good reason. Depending on the actual chance.

artificial market that has a very limited lifetime now that everyone has
realised that it's a cartel cheating them.

Exactly. "Ooo, you have to buy our diamonds. Our diamonds aren't
'bloody'." Cartel. Cheating.

Buy rubies, =A0you can't fake them or manufacture them.

Because they provide similar look? I notice you mentioned investment,
are we sure that somebody posting in _jewelry_ is looking for
investment? Though Wikipedia mentions downward pressure on ruby prices
in the 1990s so maybe you aren't thinking of them for investment.

And I'm confused about not being able to manufacture ruby. Because you
can. Though "fake" ones seems to be frowned upon. Is there good reason
for that? Again, back to Wikipedia, they mention that a completely
flawless ruby will be suspected of being artificial. Suspected, not
known. So clearly I'm missing something here. Or are we just talking
CDs vs. vinyl or a fondness for provenance? And I'm not sure "ewww, I
don't want it because it doesn't have junk in it" sounds a likely
argument for a clear gem stone.