Hi:
My first reaction was that it bears a moderate similarity to a series Vicke Lindstrand did for Kosta: the same streak of colour, the same ground out pontil, sometimes called the Contour or Kontur line. I can't locate a triangular one listed anywhere and the piece isn't signed so I'm offering this quite tentatively. I searched for the Max Verboeket vase in the earlier posts but most of the relevant pictures have gone. I still think it looks more like Lindstrand than Verboeket. Not Stroberghsyttan.
David