Thank you for the new photos. If you rub two pearls together (from opposite sides of the strand) do they seem rather rough (gritty), or are they very smooth? If rough, most likely they are akoya cultured pearls. As Akoyas age, they do darken. Looking at your pearls in person, are they more creamy and lighter than the photos?
Are you planning to wear them? Unless they've been restrung recently, that might be something good to do and have them knotted between, although at the time knotting wasn't always done. Some of us have learned to knot our own pearls, which is not difficult to learn if you like doing crafty projects. Instructions are found under the "lowly beaders" thread.
It's impossible to see the condition and quality of the nacre from the photos. You can do a search on ebay for "vintage akoya necklace", to get an idea what they are selling for. Having a clasp that is 14K or 18K gold adds value, too.
These were my grandmothers and my mother said my grandfather got them for her when he was stationed in Japan after Pearl Harbor. This is the original clasp, it does say Japan on the back. Any information about what they are or there value would be welcomed.
