
Yesterday I was helping a friend get the most money for her old gold jewelry. She is moving out of country and gave me small collection of assorted gold rings and chains that she wasn't wearing any more and figured she could use the money toward her trip.
I used the connections I have made over the years from selling my metal detecting finds to gold refiners and jewelers to get her the best price for her gold.
One of the rings had 4 pretty large diamonds in it - not huge or anything, but big enough, and they were of very good color, cut, and ok clarity. I had my jeweler pry them out of the ring and spent the day shopping them around to various jewelers and gem dealers in the gem district at Victoria & Dundas St. to see if I could sell them to maximize the money my friend could get.
I sort of knew that diamonds lost most of their value once you bought them at a store, except of course for any diamonds over a carat in size. My friend's diamonds ranged from 1/4 carat to 1/2 carat and would be more than enough for a sparkly engagement ring for someone I thought.
Unlike gold, it turns out that diamonds have no measurable value when it comes to re-selling them. But when it comes to buying them, there is a price guide called the Rap report that jewelers and manufacturers use as a guide when purchasing diamonds from wholesalers or to roughly establish value of a diamond.

This, however is just a guide that a jeweler would use to price out a ring if you wanted to get a ring made.
If you went to a jeweler to get a ring made for your fiance; say with a 1/2 carat diamond in it, he would look at this chart, call his diamond dealer, see what the dealer has on hand, and with some haggling buy the stone using the prices in the Rap sheet as a benchmark. He would get the best quality stone within the quality range you were looking for and your budget.
Then he would build your ring and set the diamond in it, probably marking up the diamond 100% in the process, adding the cost of the gold or platinum used, marking that up, and then adding his labor cost to the total.
Jewelry making is an art. It involves precision work and fine manual dexterity but also machinery and working with blowtorches, furnaces, kilns, and with toxic industrial chemicals and acids. This where a lot of the cost gets added to the final cost of the engagement ring, and rightly so, and how a ring made with hundreds of dollars worth of materials ends up costing thousands of dollars.
That much is easy to understand.
But say the engagement is called off. The dude can try and sell the ring privately, but few people want to buy a used engagement ring (they reckon it's cursed). Since the dude had it custom made, his market for resale is further reduced by his taste in ring design.
There are some sites on the internet that resell engagement rings, but generally speaking, the dude would be looking at getting less than half of what he paid to make it, minus the websites appraisal and selling fees.
So what is left is prying out the stones and melting down the metals for resale, which brings me back to the beginning of this story. The metal is easy to sell, but the stones? Not so much. It turns out when it comes to re-selling them, they have no value at all, there is really no secondary market for loose diamonds.
As for my friend, I suggested she re-purpose them. It will probably be the best bet. Perhaps she can have them made into stud earnings or something.