Water, earth and air

[Jorge_Stolfi]

WARNING - AI GENERATED STUFF

This is what Google AI Mode says about the regional use of those wolkenbands:

• Germany & Bohemia: Wolkenbands are characteristic of the International Gothic style, which flourished in major artistic centers like Prague and Nuremberg. They appear frequently in Weltchronik (world history) manuscripts and large liturgical Bibles from this region (e.g., those completed around 1415).
  
• England: English artists adopted the "nebuly" (cloudy) line patterns that form the basis for wolkenbands in works such as Gower's Vox Clamantis and manuscripts by Christine de Pizan.
  
• Flanders/Netherlands: Burgundian and Flemish illuminators used these bands to frame heavenly visions, often rendering them with the thick, knotty edges and 3D appearance you described.
  

I hope those references are not hallucinations. Goggle AI Mode seems to be more sober than other lalamos...

(But then it spontaneously added a couple of parags about the use of wolkenbands on the Voynich Mauscript.  Argh. I can't way for this riddle to be solved so that we can start to clean up all the pollution it leaked all over the internet...)

All the best, --stolfi