I named it that as I believe it's been passed down from my great-grandparents, who were Swedish immigrant farmers in Minnesota. Seems someone in the family told me the quatrefoil design is Swedish. Upon investigating its origins, I too thought it might be Clevenger, but could not find a match. How do you know it's of "quality"? And that it was blown into a mold? (the pontif mark?) And what makes you say earlier 20th century? Thanks for the input!