Ron I agree with HWooldridge, I take my steel to near white if it is sparking your burning your steel and can make your weld look ugly. I find if you are using coal that the impurities can cause problems with your weld, I make sure I only have coke in the fire and keep the coal on the outside to make more coke. A lot of times I will make bar shoes and not even use flux, placement in the fire is important you do not want it to deep it will just oxidize the steel and frustrate you when your weld fails. I keep about 4" of coke under the steel and at least that much on top usually more though.