I can't speak to Cartier because I haven't shopped with them, but Tiffany's round diamonds are almost all triple Ex - and even their melee is full cut. I think it is generally assumed at Tiffany's that the diamonds are EX cut unless you ask. It is worth checking not assuming, obviously, because they aren't all EXEXEX, but they have much higher standards (on average) than just about anywhere else.
Also, why is nobody discussing ethics? For me that is the #1 reason to buy a branded diamond, if I know the brand is involved on a deeper level in ensuring the diamonds are acquired ethically (like Tiffanys). If you're buying non-branded you MUST buy Canadian.
Also, why is nobody discussing ethics? For me that is the #1 reason to buy a branded diamond, if I know the brand is involved on a deeper level in ensuring the diamonds are acquired ethically (like Tiffanys). If you're buying non-branded you MUST buy Canadian.