I am absolutely in love with this ring. 
 
The central old mine cushion cut diamond is white, bright and clear, a really nice stone, claw set to the middle of the ring. The spiralling surround is early 20th century, French, made in 18ct gold and platinum, and set with tiny rose cut diamond highlights. 
 
French eagle head hallmark to the outside of the shank, in the  typical French way. Tested as 18ct gold and platinum.
Weight approx 4.41g
Principle diamond calculated to be approx 0.45ct, Estimate of F/G colour, VS clarity. 
Tested as natural, earth mined diamond .
Overall width at the front approx 13mm
Shank width at the back approx 1.4mm
Finger size UK  O1/2 (approx USA size 7.75)
Excellent antique condition, evidence of historical resizing, and could be resized again.