Cobalt blue glass mantle luster candle lamp Mary Gregory?

I have a beautiful blue glass mantle/luster candle lamp. It is quite large, measuring 11" tall & approx 18" round at the top. I haven't been able to find any identifiable marks, but believe it may be by Mary Gregory. I have searched quite a bit online & haven't seen another like it. I just purchased it in eBay at a very good price. I collect cobalt glassware & would love to find out more about this piece. I have no idea the age, maker, or worth.