This was my grandma's covered syltetøy jar. The bottom is marked only with the Stavangerflint logo and "Norway." I don't know who this designer was.
You'll notice the small smudge at about 3:00 on the Stavangerflint logo. I used to think those were just smudges, but I recently read that there was a pattern to them - but no one seems to know what that pattern was! One contemporary pottery studio, Ephraim Faience from Wisconsin, uses a similar method to indicate the year of production (a hatch-mark at 3:00 meant it was produced in 2003). I assume the Stavangerflint mark was used in a similar manner. The glaze marks seem more prevalent on the older pieces. Now we just have to find out what they considered year-zero.