Damn, I'm happy the tradition in much of Europe are just plain gold bands for engagement rings, like wedding bands. You just move it from one hand to the other at the time of marriage, or get a similar wedding band.
Few things depreciate as badly in value as jewellery does. I would do this:
- Get some technical knowledge and impartial advice, particularly when you've picked a few candidates. Neat trick: Make a deposit and take the candidate to an auction house or a dealer in antique jewllery - they normally do free valuations, and normally won't mind looking at it at all. It's part of their business plan to provide the service. This would also render a gemmologist's certificate unnecessary - you can always get a new valuation with a certificate later, if necessary.
- Buy from a reputable auction house or specialist dealer. A trip to the New York or Antwerp diamond districts is very educational, and might offer a good deal. Buy vintage, and if you plan to buy for the stones, seek out formerly really expensive jewellery in as bad a taste as possible, and then chuck the brooch/stick-pin/pendant. Or buy a good ring as it is.
- Have the ring restored or re-set at a good jeweller's, if necessary. These very often do not have store-front shops, just hidden-away messy workshops.
A few thoughts:
- The importance of the difference between old- and new-cut brilliants is overrated. An old-cut diamond with a good precise cut can be far nicer than a new-cut one. The rarer cuts, like baguette, marquise, rose-cut etc. can sometimes be bought for far less. One of the tricky points of a brilliant-cut stone is that they rarely can be re-cut without a significant reduction in size. This makes re-cutting brilliants almost pointless, but can in some cases heighten the value of other cuts, particulary the oblong ones, like baguette and marquise.
- Few people are able to discern slight imperfections in a stone. If you can't see them, and practically noone else can, what's the point of paying for perfection? Not a very romantic thought, I know, but this is really about getting practical value for money.
- The idea that it's bad luck to buy an old/second-hand/used engagement ring is another part of the deBeers mythology. Don't listen to it - fantastic pieces of antique jewellery have been destroyed because of the idea. Apart from that, an old piece will very often have a far better setting and general goldsmith's work. No point in destroying it, if not absolutely necessary, for reasons of taste or other.