I have recently inherited a filigree engagement ring and wedding band from 1929/1930 (the wedding band is inscribed 11/1930… so I assume the engagement ring is older). It was my great grandmother's. Ive yet to have it appraised because I have no intentions of selling it; I would love to keep it in the family. The ring is set with one center stone, and two small stones on each side. One of the smaller stones on the side is missing…
Would it decrease the value of this antique by replacing the stone?
(While I have no intentions of selling it, I would like to preserve it as best as possible)
My sense from years of watching 'Antiques Roadshow' is that the value loss happened when the stone was lost, and that if it's replaced with one which matches in the '4 Cs' – color, cut, clarity, and carat (weight) – some or even most of the value actually will be restored.
Look for a jeweler who does conservation or restoration work, not just making or selling jewelry – they're not the same thing. I assume that the fact that a stone was lost means that SOME kind of repair to the setting will be necessary, and that needs to be in keeping with the original work.
Even though you have no intention of selling, you might still want to consider an appraisal – your insurance company would probably require one if, heaven forbid, you had to file a claim for loss of the piece. A good appraiser can often offer guidance on making repairs, too. There's a link to appraisers on the Roadshow's website, along with a lot of other useful info.
http://www.pbs.org/wgbh/roadshow/resources.html
Good luck, and enjoy your wonderful heirloom.