Surface mix torch
From Melting Pot Wiki
Surface mix torch: A torch in which the gasses mix at the surface of the torch, as opposed to a premix torch in which the gasses mix in a chamber. Surface mix torches provide more complete combustion of the gasses than a pre-mix torch, which allows for a better flame atmosphere. The atmosphere of a surface mix flame is more suitable for using in most colored glassses than a pre-mix torch. Surface mix torches do not require a flashback arrestor or check valves like pre-mix torches do.