Antique diamond single stone ring with a pear-shape rose cut diamond

Antique diamond single stone ring with a pear-shape rose cut diamond measuring approximately 10.5mm x 8.5mm in a closed-back gold setting with pierced gallery on tapered gold shank. Ring size approximately M. We believe the ring to be antique and probably late 19th/early 20th century. Not hallmarked but probably 18ct gold. The closed back setting restricts measuring the depth of the stone, the depth including the setting is approximately 7.3mm. The diamond is a lively stone that appears to be of good colour and clarity, no obvious inclusions, small inclusions when viewed with a loupe, one small white inclusion only just visible to the naked eye but not obvious. Colour and clarity difficult to estimate due to the restrictions of the setting. Weighs approximately 8.5 grams.