Black iron oxide (Fe3O4). Common source of iron.  Melts at low‐fire temperatures. Red iron is finer in particle size than black. Iron is usually tan to brown to red‐brown in oxidation, but can also be amber in lead glazes, or glazes with Barium or Strontium. Yellow to olive in high alkaline glazes. In reduction 1‐6% with Calcium phosphate gives blues, ½ ‐3% with some Calcium gives celadons, 10‐15% Temmoku.