Another "hidden" reaction has been found!
If BMTL has a tmp of 2, it will turn nearby IRON and METL into BMTL with tmp=1.
Do any reactions create BMTL with tmp=2?
@12Me21 I am guessing that is how salt, salt water, and oxygen rust multiple layers of iron. Just a guess though.
@ChargedCreeper is correct. It's used in rusting.
Place a particle of salt on a block of iron and step through frame by frame, examining the BMTL that is formed.
BMTL with tmp>0 represents rusting metal. BRMT represents rust.
BMTL tmp decreases with time.
tmp>1 particles spread the rusting, sending tendrils of rusting BMTL into the iron. tmp=1 particles do not spread, and turn into BRMT after a random delay.