Amsterdam had its own, rational Art Nouveau variant. This was fueled by the theosophical movement then in vogue. Designer-architect Mathieu Lauweriks was a leading representative. Klaas van Leeuwen also moved in these circles. I wrote an article on his 1907 "Letterboek"; it was recently published open access in "Quærendo" (link below). There will be a small edition brochure soon, partly set in @HEX Lauweriks.
https://brill.com/view/journals/qua/55/2/article-p141_3.xml

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