Can I use a diamond from another piece of jewelry in my engagement ring?

Usually, yes, and anyone who tells you otherwise is trying to sell you a new diamond. Using a diamond from another piece of jewelry in an engagement ring is one of the oldest moves in the trade, and I've done it enough times to know where it goes wrong. I've pulled workable stones from cocktail rings, earrings, tie pins, and one truly hideous 1980s necklace. The stone itself doesn't care where it lived before. It cares about its girdle, its culet, and whether its depth will fit a setting you can wear every day. A stone that already survived decades in a ring has proven something. A stone from a necklace hasn't proven anything yet.

Last fall a woman named Rachel brought in her grandmother's engagement ring. The center was a 1.07 carat old European cut, J color, SI1, and it had a small chip on the girdle at the 10 o'clock position. She wanted the stone in a modern six-prong solitaire. I told her no. A six-prong solitaire would leave that chip exposed, and the first time she caught the ring on a sweater or a drawer pull, she'd lose a piece of the stone in the first year. She didn't like me that day.

We settled on a half bezel with one prong rotated to cover the chip. That single design change cost about $180 extra. The ring came back from the bench looking better than the original piece, and Rachel later admitted she only resisted because she'd already saved six photos of a classic solitaire on her phone.

Four things I check before I say yes

• The girdle. A thin girdle is the most common reason I turn down a repurposed diamond. If it's been worn for forty years and someone polished it too aggressively, the edge can be fragile. A small chip can be hidden under a prong. A paper-thin girdle cannot.
• The depth. Older cuts tend to be deeper than modern stones. A 1.00 carat old mine may have the face-up spread of a 0.80 carat modern round. That's fine if you know it going in, but it changes the look.
• The wear. Surface abrasions and small nicks are normal on stones that have lived in a ring. Most polish out for $150 to $300. A broken culet is different. That usually means re-cutting, and you lose weight.
• The report. If the stone doesn't have a GIA or IGI report, I'll send it out before quoting a setting. Not because the stone is suspicious, but because I want to know exactly what I'm working with before I tell a client the final price.

I have a soft spot for old European cuts and old mine cuts that came out of pieces from the 1920s and 1930s. They were cut for candlelight, and they still glow in low light in a way a modern round brilliant often doesn't. I would rather set a J color old European with a visible chip I can hide than a D color modern round with a mediocre cut and a lab report that says ideal but isn't.

Re-setting a stone you already own costs less than buying a new diamond, but it isn't free. A basic 18k yellow gold mounting, six prongs, size 6.5, runs about $350 to $700. Custom CAD and casting pushes that to $1,200 or $1,800. Re-cutting adds $350 to $600. If the stone has no lab report, add $75 to $150 to get one from GIA or IGI before you commit to a design.

One note if the diamond is coming from an earring: check for a drill hole. Some earrings are set with stones that have been drilled for a wire. If that is the case, the hole can't be undone, but a bezel or a clever prong can cover it. Those jobs are more fun than they sound.

If the source piece still gets worn, don't cannibalize it yet. I had a client named Daniel who brought me his late mother's diamond cocktail ring and asked me to pull the center stone. He was fine with it until I showed him a photo of the ring as it was. Then he couldn't do it. We ended up buying a similar 0.90 carat old cushion from a dealer and resetting that instead. Photograph the original first. You might change your mind.

The best ring I made this year started with a diamond from a broken 1940s brooch. The client wore it to her wedding and didn't take it off for three days. Her new husband still doesn't know the stone is older than both of them combined. That's the point.