yeah, ive never used coal but it looks a little messy, propane is damn good if you have an efficent burner (i have a vacume cleaner reversed on mine for a blower and it works good)
im only using greensand, its pretty good though my castings (depending on the pattern and if im bothered to make it nice or not) come out just as smooth as my friends who uses petrobond and i think the little shower of copper wasnt caused by the moisture, i dont really know where it came from but i thought it came form in the crucible :shrug:
i added enough copper brazing rod with phosphorus in it so that there was about 1% phosphorus which is meant to stop the air sticking to the copper, i also used a flux that has a degasser in it so i put the fluz in at the last minute, quickly mixed it, scraped out a little slag and poured it fast as i could but then i dont really know for sure that theres no oxygen in it and its probly microscopic if there is any anyway
i attached some better pics, hopefully by the time the blocks been machined ill have a decent camera
