It certainly has a similarity to the Ysart paperweights but the blue mottled background put me off - as did the fact that it was one of 8 paperweights picked up for £40. I had been wondering about some of the Ysart apprentices who went on to become masters in their own right, such as William Manson, John Deacons or Peter Holmes. I thought it might be a Caithness weight but apart from having gone through the complete Caithness Paperweights catalogue and not finding it, the base points more in the direction of Vasart/Strathearn rather than the flat, polised Caithness base.
John