Roger, could you please give various dimensions for this item. Ideally I would like to know measurements along the lines of those I gave in a post in a thread about an unusual bottle
I would also like to see a side on photo of the full stopper and its shank.
And does the stopper fit well in the neck, or is it rather loose?
Although the majority of Salvador Ysart inkwells had striping to the stopper, the neck and the well section, there are examples which have clear glass in those parts, but for which the overall dimensions, shape and finishing line up with the more typical "striped neck" versions. In such cases, they are normally referred to as "Vasart" (meaning Ysart Brothers period).
But as Alan has said, there are others which are either called friggers or classed as Unknown Maker. Many of the unknown maker bottles include Strathearn canes as well as early Ysart ones, but the examples with only early Ysart canes are not so easy to identify or give a date to.
I have checked three or four examples of bottles like yours, including one of my own, under uv and they have reacted the same as for Ysart Brothers or earlier. All of the usual "Unknown Maker" bottles I have looked at under uv did not react as Ysart Brothers or earlier - and they did not react as Vasart Ltd or Strathearn, either, which lines up with Alan's point about some items being made elsewhere.