This antique diamond has been reset into a contemporary styled mount at some time during the 1990s.  It is a rub-over/collar in an 18ct white gold cylindrical mount to an 18ct yellow gold shank that has raised strap-work panels to the shoulders. 
 
With an in-vogue retro styling, the ring is perfect as an engagement or right hand ring that combines the antiquity of the old diamond with the more modern lines of the setting. 
 
The diamond is approx.  0.20ct and the band is18ct yellow gold.  It will fit a finger size L (UK), 6 (US) and  may be resized.