Congrats on presenting a diamond-alternative to her. The diamond trade is absolutely disgusting and unfortunately many people seem to equate "love" with a shiny rock. If it came down to it, I would have to reevaluate marrying someone that refused to believe otherwise.
I started thinking about this issue a few days ago and have yet to come up with a strategy for convincing a (future) partner on the follies of purchasing a diamond. Is there any recourse at all to the epic marketing job De Beers has masterminded?
1) Make jokes about diamonds being bad long before there's thought of engagement rings. Get your friends, hopefully her friends, and ideally her to do the same.
2) Make it clear that your objection is not to financial. If you do go with a gem that proves to be less expensive, donate the balance to a cause she believes in. If you do have financial objections, express them separately, in financial terms; don't conflate the issues.
3) Point out that it is not a long-standing tradition, but rather a recently manufactured one.
Artificial diamonds are solid, physical proof of the achievement of mankind. We've taken the most regular, durable objects that nature can produce and we've duplicated and bettered them. Every time you look at an artificial diamond, that's science, right there, concentrated and almost literally crystallized.
My SO has agreed to being given a kitten as an engagement gift. I think it works great as a replacement. Not cheap (food, needles, etc), not short-term, and cute. She'll probably enjoy it more than the 30 aggregate minutes of showing off a ring, too.
Find someone who's not into that whole thing. Not everyone is the same. There are highly ethical people, vegans, "occupy" people, hairy feminists, eco-warriors, punks, goths, nerds, socialists, anarchists. There are loads of people who will pride themselves on not having a diamond. There are people who don't fit in these common moulds.
Hehe, I suppose I was trying to allude to more extreme feminist leaning people.
(Pedantically, I could claim we are all feminists, after all, nearly everyone here thinks women should be able to vote. But that wasn't the meaning I had in mind initally)
Pedantically? Pedantically, feminism encompasses much more than the right to vote, which is why not all people are feminists. Having the right to vote would be suffragism. :)