Daim ntawv thov:Tshem tawm cov tsis muaj zog hlau nplaum los ntawm cov ntaub ntawv zoo thiab ntxhib hmoov, nws tau siv dav hauv ceramic, iav, tshuaj lom neeg, kev lag luam refractory thiab lwm yam. Lub caij no nws kuj tuaj yeem siv rau hauv kev ua cov hematite, limonite ect, tsis muaj zog hlau nplaum.