My apologies for not responding sooner I have been out of action for a year but getting back to it this summer! I use a Propane Sievert Torch with Sievert 3941 High Precision Burner - Medium to Large burner head, It produces a lot of heat and a bushy flame. Never take the flame off the billet until fusion occurs to reduce any oxygen present. I also build a cave of firebricks and keep the billet and clamp small. The temp of he torch is not so much the issue as making sure to get an even and thorough heating of the billet. good luck and I hope I am not too late to help.

@@therecycledmetalsmith Thanks for your answer, it helps me a lot

My apologies for not responding sooner I have been out of action for a year but getting back to it this summer! No I do not compress again, however I do know of people that like to hammer the billet after coming out of the clamp and while still hot. It would be worth experimenting.

My apologies for not responding sooner I have been out of action for a year but getting back to it this summer and I hope I am not too late to help. Yes I absolutely love the Sievert!! it is a very useful torch so long as you have a range of heads. I nearly always use for annealing, Mokume Garne and for melting material for billets. It just uses ambient oxygen from the air and does not need extra oxygen. BTW I use an oxygen concentrator for my Little Smith and that's is proving very economical after the initial outlay.

Absolutely correct John, thank you.