I'm not totally convinced either but Riihimaki did make a tapering cylindrical vase a bit like yours Andy (in the late 60s/early 70s) however it was much larger, more like 10 inches in height - I had one once in red but I don't know if they made them in smaller sizes. The polished pontil would also be wrong for Riihimaki. Can we see a photo of the base please?