Roy's gloves are made of a cloth called ignition cloth, or spark cloth. When rubbed together, with enough force, it induces a spark, then he changes the density of O2 in the air, which is very flammable.

I'm gonna leave the way the transmutation circle works to Nature Path Alchemist, because it was suggested to him.

I tomorrow, I will explain Auto-mail, and materials, and different types of it.