alum
礬 centers on alum, a specific mineral compound used in dyeing, medicine, and water purification.
礬 combines 石 (stone, mineral) with 樊, which likely contributes the sound. Together they indicate a mineral substance, specifically alum.
The bottom 石 (stone) tells you it's a mineral, and the complex top 樊 looks like a tangled chemical structure. Picture a lump of alum crystal with a complicated lattice on top.
For バン, imagine a van full of alum crystals: van -> バン, and the stone-like mineral is loaded in the back.
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alum
potassium alum
chrome alum
alunite
bauxite
grossular; grossularite
amblygonite
zinc sulfate heptahydrate; white vitriol
alumina
gedrite
melanterite (FeSO4-7H2O)
blue vitriol; chalcanthite
pickeringite
pyrope
bieberite
bauxite
almandine