Greetings from a new member. I have always had a soft spot for pearls and have many strands in my collection. My husband likes to surprise me with a new necklace every now and again, and recently purchased this Mikimoto pendant necklace from a private estate. There is no paperwork, tags or receipt to authenticate his find. Did the tooth test and the pearl is real, but the pendant itself isn't marked anywhere. The necklace is marked K18 with the M inside of the shell. Does this look correct? Any idea of when Mikimoto used the red boxes? Many thanks in advance.