I was given an 18" strand by my mother about 10 years ago and they are in their original box with certificate book dated 1/29/1969 stamped with the M logo & SL. She said they were valued at $1200 back then. I am looking to get them revalued and i don't know how to go about it. I am may sell them, but would prefer to decide after a valuation. Do they gain or lose value over the years? I have attached photos for ya'll to help me out as i am at a loss with who in Houston, Tx, can help me. The pearls are originally from Australia and the certificate booklet was printed in Sydney. They start at 2mm and goes up to 7mm in the front center and have a creaminess in color.