My great grandmother's slag glass lamp from 1908. Unknown maker.

My great grandmother lived in Chicago from 1888 until 1929. The family then moved to Cincinatti where they lived until the late 1940's. I would imagine the lamp was purchased new. It is definitely real slag glass as you can tell by the sound when tapping on it. The base is very ornate and very heavy. It is in nearly perfect condition with no cracks to any panels and only a few very small chips in the white finish on the base itself. I put a new cord on it when I inherited it back in 1991, but all other hardware on it is original as far as I can tell. I did find what I think is a manufacture date of 1908 on it, but no other markings as to the manufacturer. I would never sell this lamp, but I would be interested in determining its worth for insurance purposes. I would also be interested in finding a matching lamp so I could have one on each nightstand.