The effects of compounding ingredients on the sulfidization reaction of brass were studied by GPC and TOF-SIMS using a squalene reaction medium. The absence of both carbon black and cobalt salt retarded the decomposition reaction of the accelerator as well as the crosslinking reaction of squalene. Replacement of squalene with its saturated counterpart, squalane, suppressed the accelerator decomposition, the formation of copper sulfide layer and the formation of the cobalt-related compounds in the adhesion layer. The formation of the copper sulfide layer was enhanced by the absence of cobalt salt.