Silica fume is also called microsilica, silicon ash, condensed or densified silica fume, its color is grey. Silica fume is also called microsilica, silicon ash, condensed or densified silica fume, its color is grey. This is a byproduct of producing silicon metal or ferrosilicon alloys, which is made in the furnace with quality quartz, coke and scrap iron. Silica fume used in refractory can ...