This study was conducted by the Bureau of Mines to determine the effect of steel reheating practices in burning natural gas on the amount of silicon required to prevent the formation of copper on steels containing up to 1 wt-pct cu. Formation of copper, which causes surface hot shortness, was readily prevented by as little as 0.3 wt-pct si and by 2 vol-pct excess oxygen in the furnace atmosphere when reheating steels containing up to 0.8 wt-pct cu. Up to 0.8 wt-pct si content and careful control of reheating conditions were necessary for steels containing 1 wt-pct cu. Best conditions for these steels were reheating to 2,200 deg f (1,205 deg c) in burning gases containing 2 vol-pct excess oxygen, and then to higher temperatures in gases of 6 vol-pct excess oxygen. Slag and mold wash were not detrimental on steels reheated for 8 hr by a soaking- pit-type furnace schedule, but they were problematical on steel heated for 2 hr by a pusher-type furnace schedule. The effect of silicon contents on scaling rates also was determined.