Because epoxy resin dries so slowly ... to recreate another aspect of nature (the Earth itself). Just DIY some geode designs with colors you like, as demonstrated by @artisttilldeath on TikTok ...

Pretty soon he was using silicone rubber to make two-piece, high-quality molds of lenses, good enough to try a few casting shots with epoxy resin. [Zach] ran into a few problems along the way ...