holmium, pattern on sword blade
錵 centers on a decorative pattern on a sword blade, created through differential hardening. The holmium sense is a modern chemical element name assigned to this character, unrelated to its original meaning.
錵 is a Japanese kokuji (国字) created by combining 金 (metal) with 花 (flower) to represent the flower-like pattern on a sword blade. The reading にえ is native Japanese, while カ is a later assigned on-reading. The holmium meaning is a modern borrowing from Chinese, where the character was repurposed for the element.
Metal (金) shaped into a flower (花) pattern on a sword blade: 錵 is that decorative metalwork.
For カ, imagine a car (カ) with a custom sword-blade pattern painted on its hood: car -> カ, and the pattern gleams like metal flowers.