Age of Gold Ring

by Nise
(Nottingham UK)

i have had a ring passed down to me from a great aunt. i have been trawling the net for clarification on hallmarks but without success.

it says CPS,
then the 'gold' crown,
then 18 (i presume 18c gold)
the the ancour (which i know is Birmingham)
then a I or a T (i think it is the T)
can you shed any light on its age, and if it would be considered valuable? it is ruby and diamound (the real thing i think as you can tell the ring is quaility) i am not looking at selling, just want to know the age really
thank you