I have recently noticed the use of opalescent glass in some Selkirk vases.
It's not something many studios did use. It might be worth checking to see if there is any "fire" lurking within it. It might help confirm a Selkirk diagnosis.
But every Selkirk vase I've found has been clearly marked and dated, in small, neat, capital letters. I haven't found one with an artist signature on it though. Just marks, years and labels.