Buttery rich 18ct gold, and an old European cut diamond - just the best combination! 
This star set ring is super comfortable on the finger, and so easy to wear, day in, day out. 
This dates to the early 20th century. Unfortunately, the hallmark is worn and indistinct, so I can't make out any details. 
Tests as 18ct gold 
Weight approx 4.82g 
Finger size M (fits slightly smaller) approx US size 6
Diamond approx 0.18ct (calculated in setting)
Tested as a natural, earth mined diamond 
Width at the back approx 3.2mm 
Width at the front approx 8.4mm 
Very good antique condition