ray dilloh

I am trying to add sulfur to lead as in wiljens myth of arsenic article. How do you do this without it catching fire? He says he cooked it 1 hour at 900 degrees which is slightly above the boiling point of sulfur. I did this with a lid on the pot but aparently had too much material cause it boiled over. After it cooled I removed lid and had a pool of melted sulfur on top of solidified lead. How do you stir it without it catching fire? I added 3 lbs sulfur to 80 lbs of lead. I need advice please