I recently went to a local jeweler's estate sale. I purchased a single strand, graduated, cultured pearl necklace about 16- 18" long with a certificate and number of 'H 260' and an envelope with extra pearls. It seems in very good condition. I would like to know any information about the value or date of the necklace. I have searched for Heller, Heller & Sons, Heller-Deltah, Imperial, etc. but could not find anything more than vague references to the Heller company. Would it be possible or even likely information on the item and seller/ company still exists? What would be the $ value? When would it have been made? Thank you for your assistance.