Identifying cultured pearls

by David M Scott
(Carberry, Manitoba, Canada)

I purchased an 18in string of cultured pearls in 1961 as a wedding guest for my wife. It was purchased from a very reputable retailer that is still in business after 125 years. I was advised that they were of high quality.

The cost at the time was $100.00. They are nicely graduated and the clasp was white gold i was told. They have a very nice lustre and the colour is white to cream. I would like to know the value for insurance purposes. How can I accomplish this?
Thanks
David