Thank you for contacting Mearto with your appraisal inquiry.

It is a beautiful diamond and ring band. Such antique diamond rings are being offered at auction on a regular basis.
The stone has a lovely cut and shape however today most people want the modern cut. The design of the ring is very nice and typical of the first part of the 1900s. The condition is used and could need some maintenance but it will be worth your while to have the ring repaired.
The colour of the diamond appears to be fairly good and with some inclusions. It is hard to tell from the photo if the corners of the diamond has been damaged and have some chips this is why the estimate is with a large gap.

I believe that this ring would attract the attention of both collectors and dealers if it came up for auction and it could even surprise in a positive direction pricewise if it came up for auction.
The estimate provided is for a well-advertised specialised online jewellery auction, where I believe the ring has the best chance of realising its fullest potential. However, there is no measurement for the sentimental value you might attach to the diamond ring. Retail "asking prices" can be higher and vary.

Please let me know if you have any additional questions. I’m happy to help.
Thank you