thankfully i had the perfect amount of bricks to make a bloomery. i was concerned about how slow it was heating the flint and stopped "cooking" it in a firepit at about 600c which had used 4 black coal. A previous cook i had missed produced 14 calcinated flint (from a stack of 64) from 64 charcoal, seemed rather high but i had only seen that changes were made to smithing and didnt know it was affecting all heating times.